Mercapturic acids of acrylamide and glycidamide as biomarkers of the internal exposure to acrylamide in the general population

Acrylamide (AA), a widely used industrial monomer which is categorised to be carcinogenic, was found to be generated in starch-containing foods during the heating process. This discovery has caused reasonable concern about possible health risks to humans due to dietary acrylamide uptake. In order to gain more information on human metabolism of acrylamide and to contribute to the assessment of the human carcinogenic risk due to AA uptake we measured the mercapturic acid of AA and its epoxide glycidamide (GA) i.e. N-acetyl-S-(2-carbamoylethyl)-L-cysteine (AAMA) and N-(R,S)-acetyl-S-(2-carbamoyl-2-hydroxyethyl)-L-cysteine (GAMA) in human urine. The relation between AAMA and GAMA is important in this context because GA is thought to be the ultimate carcinogenic metabolite of AA. The median levels in smokers (n=13) were found to be about four times higher than in non-smokers (n=16) with median levels of 127 microg/l versus 29 microg/l for AAMA and 19 microg/l versus 5 microg/l for GAMA. Therefore cigarette smoke proved to be an important source of acrylamide exposure. The level of AAMA in the occupationally non-exposed collective (n=29) ranged from 3 to 338 microg/l, the level of GAMA from <LOD to 45 microg/l. The ratio of GAMA:AAMA varied from 0.03 to 0.53, median was 0.16 which is in reasonable agreement with results of different studies on rats. Thus the metabolic conversion of acrylamide to its genotoxic epoxide glycidamide seems to occur to a comparable extent in rats and humans. Consequently, risk estimations by various authorities based on experimental data obtained in rats are supported by our findings. Besides we also measured the haemoglobin adducts of AA and GA in the blood of 26 participants. From these results compared to the mercapturic acids, we deduce a steady state for AA uptake, and we demonstrate a higher reactivity of GA in comparison to AA towards haemoglobin compared to glutathione in humans.

[Sevelamer:hydrochloride]

The recent global breakthrough in the field of renal osteodystrophy is the inhibitory effect of sevelamer hydrochloride on the progression of coronary artery calcification, which was revealed with EBCT (Electron beam computed tomography) 1) approximately 3). It has been found that the degree of coronary artery calcification assessed with EBCT is proportional to the mortality risk by the coronary artery stenosis and by myocardial infarction in non-hemodialysis patients 4) approximately 10). In 2004 in Japan Matsuoka and Iseki et al showed for the first time in the world that coronary artery calcification assessed by EBCT was correlated with mortality 11). In Japan, however, it is difficult to administer sevelamer hydrochloride to many patients because of constipation as its side effect. Its prescription rate is 26.8% and its single administration rate is only 15.4% 12). We explained fully to the patients that sevelamer hydrochloride seldom caused coronary artery calcification. And we used sorbitol, an osmotic purgatives, with sevelamer hydrochloride. Moreover, we gradually replaced calcium carbonate with sevelamer hydrochloride in supper at first. With protocol above, we succeeded in having 86.7% of the patients take sevelamer hydrochloride 12). We think that it is important to increase the intake rate of sevelamer hydrochloride in order to prevent coronary artery calcification and to aim at the long survival of the patients.

[New therapy strategies in secondary hyperparathyroidism on dialysis (I): new concepts, new treatments]

Secondary hyperparathyroidism (SHP) is still an early and frequent complication of chronic renal disease (CRD). Currently, CRD is an independent cardiovascular risk factor, and calcium-phosphorus metabolism is one of the modifiable related factors. In this first article, we summarize the recent SHP treatment paradigm shift in dialysis patients, derived from the better knowledge and understanding of vascular calcification. We analyze the most recent guidelines (K/DOQI), and describe the general implications of hyperphosphatemia, as well as our therapeutic approach with phosphorus-binders. Since sevelamer additionally presents some pleiotropic effects and it attenuates the progression of vascular calcification, we consider it in the first-line of treatment despite it is not yet demonstrated a survival benefit. We also minimize the use of elemental calcium to a maximum of 1000 to 1500 mg/day. Lanthanum carbonate may well be an important therapeutic agent in the near future, especially if security concerns related to metal accumulation are overcome. Ferric citrate, colestilan and nicotinamide may soon play a role. All these drugs, isolated or in combination, are important in the treatment of SHP since a great deal of its success and the avoidance of some dialysis-related complications depend on an efficient phosphorus control.

Dose-dependent transitions in mechanisms of toxicity: case studies

Experience with dose response and mechanisms of toxicity has shown that multiple mechanisms may exist for a single agent along the continuum of the full dose-response curve. It is highly likely that critical, limiting steps in any given mechanistic pathway may become overwhelmed with increasing exposures, signaling the emergence of new modalities of toxic tissue injury at these higher doses. Therefore, dose-dependent transitions in principal mechanisms of toxicity may occur, and could have significant impact on the interpretation of reference data sets for risk assessment. To illustrate the existence of dose-dependent transitions in mechanisms of toxicity, a group of academic, government, and industry scientists, formed under the leadership of the ILSI Health and Environmental Sciences Institute (HESI), developed a series of case studies. These case studies included acetaminophen, butadiene, ethylene glycol, formaldehyde, manganese, methylene chloride, peroxisome proliferator-activated receptor (PPAR), progesterone/hydroxyflutamide, propylene oxide, vinyl acetate, vinyl chloride, vinylidene chloride, and zinc. The case studies formed the basis for technical discourse at two scientific workshops in 2003.

Efficacy and side-effect profile of sevelamer hydrochloride used in combination with conventional phosphate binders

BACKGROUND

Poor phosphate control is common among patients with end-stage renal disease. Sevelamer hydrochloride has been demonstrated to be a safe and effective phosphate binder when used as a monotherapy. However, cost limits its usefulness in many countries. Data assessing its effectiveness and safety in combination with conventional phosphate binders are lacking.

METHODS

Dialysis patients meeting the following inclusion criteria participated in this study: (i) hyperphosphataemia >1.8 mmol/L (5.6 mg/dL); and (ii) an inability to tolerate currently available binders. The trial was conducted in three phases each lasting 3 months: (i) an observation phase (patients continued on their regular phosphate binders); (ii) a titration phase (sevelamer was added at a dose of 403 mg three times daily with meals, titrated to a maximum of 1209 mg three times daily); and (iii) a maintenance phase.

RESULTS

Twenty-five patients were recruited into the study. Eighteen patients completed all three trial phases. Mean serum phosphate dropped from 2.11 +/- 0.06 mmol/L (6.6 +/- 0.2 mg/dL) during the observation period to 1.91 +/- 0.01 mmol/L (5.9 +/- 0.003 mg/dL) during the maintenance phase (P=0.02). Calcium x phosphate product fell from 5.49 +/- 0.17 mmol2/L2 (68.64 +/- 2.11 mg2 dL2) to 4.89 +/- 0.27 mmol2/L2 (61.36 +/- 3.35 mg2 dL2) (P=0.02). There was no significant change in serum calcium or parathyroid hormone. Total serum cholesterol fell from 3.8 mmol/L (3.4-4.37) 147 mg/dL (131-169) to 3.55 mmol/L (2.97-4.2) 137 mg/dL (115-162) (P=0.02). Serum low-density lipoprotein cholesterol also fell significantly from 1.67 +/- 0.10 mmol/L (65 +/- 4 mg/dL) to 1.52 +/- 0.11 mmol/L (59 +/- 4 mg/dL) (P=0.04). The average prescribed dose of sevelamer was 2.4 g/day. Elemental calcium dropped from 3.4 g/day (1.4 to 4.6) to 1.2 g/day (0.6-2.4) (P=0.04). Seventy-two per cent of patients reported mild flatulence, nausea and indigestion. Three patients discontinued treatment because of adverse effects.

CONCLUSIONS

Sevelamer in combination with conventional phosphate binders is effective in lowering serum phosphate and calcium-phosphate product in patients with refractory hyperphosphataemia. Beneficial effects on lipid profile were also observed. Mild gastrointestinal upset is common.

[Evolution in vitamin D treatment after debut of sevelamer hydrochloride in chronic renal failure patients]

Newly developed sevelamer hydrochlorid (Sev-HCl) has been recognized to show the effective control of the hyperphosphatemia in chronic renal failure patients, without elevation of serum Ca, Mg, and Al as well. Then, Sev-HCl has been expected to evolute the vitamin D treatment, and to reduce the ectopic calcifications through lowering Ca x P products. Although, relatively high frequent abdominal adverse effects in Sev-HCl treatment were reported, including life-threatening bowel occlusions or bowel perforations. It is important to use the appropriate dose of Sev-HCl avoiding the abdominal adverse effects.

DNA adducts in rats and mice following exposure to [4-14C]-1,2-epoxy-3-butene and to [2,3-14C]-1,3-butadiene

1,3-Butadiene (BD) is a major industrial chemical and a rodent carcinogen, with mice being much more susceptible than rats. Oxidative metabolism of BD, leading to the DNA-reactive epoxides 1,2-epoxy-3-butene (BMO), 1,2-epoxy-3,4-butanediol (EBD) and 1,2:3,4-diepoxybutane (DEB), is greater in mice than rats. In the present study the DNA adduct profiles in liver and lungs of rats and mice were determined following exposure to BMO and to BD since these profiles may provide qualitative and quantitative information on the DNA-reactive metabolites in target tissues. Adducts detected in vivo were identified by comparison with the products formed from the reaction of the individual epoxides with 2'-deoxyguanosine (dG). In rats and mice exposed to [4-14C]-BMO (1-50 mg/kg, i.p.), DNA adduct profiles were similar in liver and lung with N7-(2-hydroxy-3-butenyl)guanine (G1) and N7-(1-(hydroxymethyl)-2-propenyl)guanine (G2) as major adducts and N7-2,3,4-trihydroxybutylguanine (G4) as minor adduct. In rats and mice exposed to 200 ppm [2,3-14C]-BD by nose-only inhalation for 6 h, G4 was the major adduct in liver, lung and testes while G1 and G2 were only minor adducts. Another N7-trihydroxybutylguanine adduct (G3), which could not unambiguously be identified but is either another isomer of N7-2,3,4-trihydroxybutylguanine or, more likely, N7-(1-hydroxymethyl-2,3-dihydroxypropyl)guanine, was present at low concentrations in liver and lung DNA of mice, but absent in rats. The evidence indicates that the major DNA adduct formed in liver, lung and testes following in vivo exposure to BD is G4, which is formed from EBD, and not from DEB.

Toxicity of propylene oxide at low pressure against life stages of four species of stored product insects

The relative toxicity of propylene oxide (PPO) at a low pressure of 100 mm Hg to four species of stored product insect at 30 degrees C over a 4-h exposure period was investigated. PPO at 100 mm Hg was toxic to all four species tested: Tribolium castaneum (Herbst), Plodia interpunctella (Hübner), Ephestia cautella (Wlk.), and Oryzaephilus surinamensis (L.). There were differences in susceptibility between the life stages of the tested insect species. Mortality tests on all life stages of the insects resulted in LD99 values ranging from 4.7 to 26.1 mg/liter. The pupal stage of E. cautella, O. surinamensis, and T. castaneum was the most tolerant stage with LD99 values of 14.4, 26.1, and 25.7 mg/liter, respectively. For P. interpunctella, the egg stage was most tolerant, with a LD99 value of 15.3 mg/liter. Generally, PPO at 100 mm Hg was more toxic to P. interpunctella and E. cautella than to O. surinamensis and T. castaneum. A 99% mortality of all life stages of the tested species was achieved at a concentrations x time product of 104.4 mg h/liter. These findings indicate that a combination of PPO with low pressure can render the fumigant a potential alternative to methyl bromide for rapid disinfestation of commodities.

Development of parenteral formulation for a novel angiogenesis inhibitor, CKD-732 through complexation with hydroxypropyl-β-cyclodextrin

The effect of hydroxypropyl-beta-cyclodextrin (HP-beta-CyD) on the aqueous solubility and chemical stability of O-(4-Dimethylaminoethoxycinnamoyl)fumagillol (CKD-732), a new angiogenesis inhibitor, was investigated with an aim of preparing a stable and effective parenteral formulation. The CKD-732/HP-beta-CyD inclusion complex was obtained in solid state by freeze-drying and characterized in solution by proton nuclear magnetic resonance (1H NMR). Then, the pharmacokinetic profile in rats and the in vivo tumor growth inhibitory activity in mice following the parenteral administration of aqueous CKD-732/HP-beta-CyD complex were compared to those of CKD-732.hemioxalate solution having an equivalent concentration. The aqueous solubility of CKD-732 was markedly increased by the combination of pH adjustment and HP-beta-CyD complexation through a soluble 1:1 inclusion complex formation, which was supported by NMR spectroscopy. The hydrolysis of CKD-732 following pseudo first-order kinetics was decelerated moderately but significantly in acidic and basic solutions in the presence of HP-beta-CyD. The stability of lyophilized CKD-732/HP-beta-CyD complex was also drastically improved after storage in various conditions. The intravenous pharmacokinetic profile and the subcutaneous in vivo tumor growth inhibitory activity of aqueous CKD-732/HP-beta-CyD complex were not significantly different from those of CKD-732.hemioxalate solution with the favorable reduction of irritation. These results demonstrate that the CKD-732/HP-beta-CyD complex is an attractive formulation for use in the parenteral delivery of CKD-732.

Determination of haemoglobin adducts of acrylamide and glycidamide in smoking and non-smoking persons of the general population

Acrylamide (AA) is a food-borne toxicant suspected to be carcinogenic to humans. It is formed in the heating process of starch-containing food. Currently, there is a great discussion about the possible human health risks connected with the dietary uptake of acrylamide. Haemoglobin adducts of acrylamide and its oxidative metabolite glycidamide are both markers of biochemical effect. However, because glycidamide has a higher carcinogenic potency than acrylamide itself, the glycidamide adduct might mirror the genotoxicity better than acrylamide adducts. In order to gain more information about the human metabolism of acrylamide, we investigated a small group of persons for the effective internal doses of acrylamide and glycidamide using haemoglobin adducts as parameters of biochemical effect. The collective was subdivided into non-smokers (n=13) and smokers (n=16) by determining the smoking-specific acrylonitrile haemoglobin adduct (N-cyanoethylvaline, CEV). The mean values for the adducts of acrylamide (N-2-carbamoylethylvaline, AAVal) and glycidamide (N-(R,S)-2-hydroxy-2-carbamoylethylvaline, GAVal) in nonsmokers was 19 pmol/g globin AAVal (range 7-31 pmol/g globin) and 17 pmol/g globin GAVal (range 9-23 pmol/g globin). For smokers mean levels of AAVal were 80 pmol/g globin (range: 25-199 pmol/g globin) and those of GAVal were 53 pmol/g globin (range: 22-119 pmol/g globin). Metabolism to glycidamide turned out to be significantly more effective in non-smokers than in the higher exposed smokers. Compared with studies in rats, the metabolic conversion of acrylamide to glycidamide as measured by haemoglobin adducts seems to occur to a similar extent in humans as in rats. Risk estimations on acrylamide based on experimental data obtained in rats obviously did not overestimate the cancer risk for the general population. Furthermore, our results might indicate that the dose-response curve for acrylamide is not linear. This would be in line with the results of animal experiments on rodents.

Effects of propylene oxide exposure on rat nasal respiratory cell proliferation

Long-term exposure of rodents to propylene oxide (PO) induced inflammation, respiratory cell hyperplasia, and nasal tumors at concentrations >/= 300 ppm, suggesting a possible role for cytotoxicity and compensatory cell proliferation in PO carcinogenesis. In this study, the effects of PO exposure on histopathology and cell proliferation in nasal and hepatic tissues were studied in male F344 rats exposed by inhalation for 3 or 20 days (0, 5, 25, 50, 300, and 500 ppm). Histopathology revealed an increase in mucous cell hyperplasia in the anterior nasal passages after 20 days of exposure (>/=300 ppm). This was associated with the formation of goblet cell nests. Cell proliferation was measured in the respiratory epithelium (NRE; mucociliary and transitional) lining the anterior nasal passages, the nasopharyngeal meatus (NPM), and the liver using BrdU administered with 3-day osmotic pumps. Significant increases in cell proliferation occurred (>3.6-fold) in the mucociliary epithelium lining the anterior nasal cavity at and above 300 ppm for both exposure periods. In the mucociliary epithelium, the 20-day labeling was commonly associated with nests of goblet cells. Significant increases in cell proliferation (>2.3-fold) were observed in the transitional epithelium at 500 ppm after 3 days of exposure and at 300 and 500 ppm after 20 days of exposure. Significant increases in cell proliferation in the NPM (>2.8-fold) were evident at 500 ppm PO after 3 days and at 300 and 500 ppm PO after 20 days of exposure. No exposure-related changes in cell proliferation were observed in the liver. These studies demonstrate a clear concordance between the site and exposure concentration for tumor induction and those causing significant increases in cell proliferation in the rat nose.

Dosimetry by means of DNA and hemoglobin adducts in propylene oxide-exposed rats

The main purpose of the study was to establish the relation between exposure dose of propylene oxide (PO) and dose in various tissues of male F344 rats exposed to the compound by inhalation. The animals were exposed to 0, 5, 25, 50, 300, or 500 ppm PO in the air for 3 days (6 h/day) or 4 weeks (6 h/day, 5 days/week). Blood, nasal respiratory epithelium, lung, and liver were collected. 2-Hydroxypropylvaline (HPVal) in hemoglobin was quantified using the N-alkyl Edman method and gas chromatography/tandem mass spectrometry. 7-(2-Hydroxypropyl)guanine (7-HPG) in DNA was quantified using (32)P postlabeling. The levels of 7-HPG in DNA of nasal respiratory epithelium and lung increased linearly with concentration as measured both after 3 days and 4 weeks of exposure. Similarly, 7-HPG in liver DNA and HPVal in hemoglobin showed a linear increase with PO concentration in the 3-day exposure group, whereas a deviation from linearity was observed above 300 ppm in the 4-week exposure group. The new results confirm previous observations of a dose difference between tissues with the highest dose present in the nasal respiratory epithelium. The measured adduct levels were used for calculation of adduct increments and corresponding tissue doses per unit of external exposure dose. For this purpose, the buildup of adducts was modeled considering the different kinetics of formation and elimination of adducts with DNA and hemoglobin, respectively, and also considering the increasing body weight of the animals. The half-life of 7-HPG in vivo, as well as tissue doses, could be solved from DNA adduct data at the 3rd and 26th days. Within the range of concentrations where the dose-response curves for adduct formation are linear, the relationship between exposure dose and resulting tissue doses could be based equally well on adduct data from the short-term exposure as on adduct data from the prolonged exposure.

Prevention and treatment of secondary hyperparathyroidism: still a challenge for the nephrologist?

Secondary hyperparathyroidism is a well known complication of chronic renal insufficency. It is not only a state of increased parathyroid hormone secre-tion but also a state of parathyroid gland hyperplasia. Prevention and treatment of secondary hyperpara-thyroidism is a huge challenge for the nephrologist, despite new agents for the treatment of hyperphos-phataemia, new vitamin D analogues and calci-mimetics. The importance of parathyroid gland hyperplasia and the possibility of its reduction frequently are neglected issues. Ultrasonography could be very useful in detection of parathyroid gland size and shape and in the management of secondary hyperparathyroidism.

Hyperphosphataemia and treatment with sevelamer in haemodialysis patients

More than 60% of patients on chronic haemodialysis (HD) have a serum phosphate level above 5.5 mg/dl (1.75 mmol/l), which recently has been recommended as an appropriate target in patients with end-stage renal disease (ESRD). Preventing hyperphosphataemia and elevated Ca x P product not only ameliorates the progression of secondary hyperparathyroidism and bone disease, but also appears to reduce cardio-vascular morbidity and mortality from vascular calcifications. Dietary phosphate restriction and the administration of aluminium and calcium salts have been the principal means of phosphate control over the last decade. Unfortunately, the protean disturbances of toxic aluminium accumulation in the body virtually eliminated aluminium from clinical practice. Calcium-based therapy, although well tolerated, results in frequent hypercalcaemia when administered concurrently with vitamin D analogues, despite a decrease in the concentration of dialysate calcium. Sevelamer (Renagel((R))) has been a novel, non-absorbable calcium- and aluminium-free synthetic polymer. In initial studies, sevelamer reduced serum phosphate, Ca x P product and parathyroid hormone (PTH) in a manner comparable with calcium acetate therapy. However, the effect on PTH levels may prove to be inconsistent. It seems somewhat less effective in binding phosphate than aluminium, although no direct comparisons have been made. In a recent study, it attenuated the progression of vascular calcification in HD patients. It also binds bile acids, resulting in substantially lower low-density lipo-protein cholesterol levels. The major obstacle to its current use is a substantial increase in the cost associated with sevelamer therapy.

Molecular dosimetry of N7-(2-hydroxypropyl)guanine in tissues of F344 rats after inhalation exposure to propylene oxide

Propylene oxide (PO) is a high-volume chemical intermediate that causes a low incidence of nasal tumors in rodents exposed to high concentrations (> or =300 p.p.m.). PO reacts with DNA forming mainly N7-(2-hydroxypropyl)guanine (7-HPG). The exposure-dependent accumulation of 7-HPG in nasal respiratory epithelium (NRE), lung and liver was determined in male F344 rats exposed to PO (0, 5, 25, 50, 300 or 500 p.p.m.) by the inhalation route for 3 or 20 days (6 h/day; 5 days/week). These exposures ranged from low concentrations, such as those potentially occurring in the workplace, to high concentrations that proved to be carcinogenic in rodents. Analysis of 7-HPG in DNA by gas chromatography-high-resolution mass spectrometry (GC-HRMS) showed a linear response in 7-HPG for all three tissues after 3 days of exposure, and for NRE and lung after 20 days of exposure. A slightly sublinear response in 7-HPG was observed in liver after 20 days of exposure. For both exposure periods, the NRE had the highest concentration of 7-HPG, followed by lung and liver. The amount of 7-HPG in NRE was seven and 17 times higher than in lung and liver, respectively, for the 3 day exposures. For the 20 day exposures, the concentration of 7-HPG in NRE was six and 13 times higher than that in lung and liver, respectively, over the concentration range studied. These results demonstrate a much higher extent of DNA alkylation in the target tissue for carcinogenesis, than in non-target tissues. As PO-induced tumor formation was highly sublinear, occurring only at high vapor concentrations, whereas 7-HPG adducts were shown to be linearly dependent on airborne concentration, these results suggest that 7-HPG is not sufficient for PO nasal carcinogenesis and that other factors such as increased cell proliferation may be important in determining the tumor exposure response.

Models of neurotoxicity: extrapolation of benchmark doses in vitro

In risk assessment, no observed exposure level (NOAEL) and benchmark dose (BMD) are usually derived either from epidemiological studies in humans or from animal experiments. In many in vitro studies, concentration-effect/response curves have been analyzed using different mathematical models finalized to the identification of EC50. In the present article, we propose a model to fit dose-response curves in vitro. The BMD approach has been used to compare the cell viability (MIT assay) of different rat (C6 and PC12, glial and neuronal, respectively) and human cell lines (D384 and SK-N-MC, glial and neuronal, respectively) after 24-hour exposure to the following neurotoxic substances: manganese chloride (MnCl2), methyl-mercury (Me-Hg), and the enantiomers of styrene oxide (SO). For all rat and human cell lines, the potency of the examined compounds was: MnCl2 < S-SO < R-SO < Me-Hg. A preliminary comparison with in vivo toxicity data for these substances gave rise to consistent results. Whereas a reasonable agreement between in vitro and in vivo data has been found for Mn and styrene oxide, a wide scatter of LOAEL has been reported for Me-Hg and these appear to be either much higher or lower than the BMD for the MIT assay we observed in vitro.

The renal dietitian's role in managing hyperphosphatemia and secondary hyperparathyroidism in dialysis patients: a national survey

PURPOSE

To survey the medical nutrition therapy practices of renal dietitians for the treatment of bone mineral metabolism.

OBJECTIVES

To obtain data on phosphorus diet prescription levels. To determine allied team involvement for phosphate binder and Vitamin D therapies. To assess the frequency and target levels for monitoring serum calcium, phosphorus, -phosphorus product, intact PTH and alkaline phosphatase.

METHODS

Two renal dietitians from the National Kidney Foundation-Council on Renal Nutrition developed a 5-question survey. This was posted on both the RenalRD Listserv and the NKF-CRN website from January 1 through February 15, 2001. Dietitians were asked to respond using facsimile, e-mail or reply by mail.

RESULTS

One hundred and thirty-one surveys were received representing all major dialysis providers in the United States, the British Virgin Islands, and Japan. Results included information for peritoneal and hemodialysis patients. Five different methods for dosing phosphate binders were determined. Prescribed phosphate binders included calcium acetate, sevelamer hydrochloride, and calcium carbonate. 108 out of 131 dietitian respondents (82.5%) have a medical protocol in place for vitamin D therapy. Of the respondents, 47% were directly responsible for implementing the vitamin D protocol. Paricalcitol was the most widely used form of IV Vitamin D. Biochemistry results were as follows: calcium, 16 different ranges from 8.0 mg/dL to 11.5 mg/dL; phosphorus, 13 different ranges from 2.5 mg/dL to 6.5 mg/dL; calcium-phosphorus product, 13 different ranges from 55-75; iPTH, 20 different ranges from 50-300 pg/mL; alkaline phosphatase, 18 different ranges from no records being monitored to a level of 500 mg/dL.

CONCLUSION

The survey revealed a large variability in the treatment of bone mineral metabolism. Improved clinical practice guidelines for the health care team are being developed with the National Kidney Foundation (NKF)-Kidney Disease Outcomes and Quality Initiative (KDOQI) bone disease management workgroup.

Sevelamer hydrochloride with or without alphacalcidol or higher dialysate calcium vs calcium carbonate in dialysis patients: an open-label, randomized study

BACKGROUND

Sevelamer hydrochloride was recently proposed as a phosphate binder to prevent hypercalcaemia in place of calcium alkaline salts in dialysis patients. So far, it has been evaluated only in patients receiving calcitriol, without comparison with CaCO(3) alone, although the latter was found to be as effective as the combination of calcitriol and Al(OH)(3) in suppressing parathyroid hormone (PTH) without inducing hypercalcaemia and to have a better lowering effect on serum phosphate. Moreover, this bile salt binder may decrease serum 25-OH vitamin D. Therefore, we compared for 5 months two strategies for controlling moderate hyperparathyroidism: CaCO(3) alone vs sevelamer in conjunction with measures to increase calcium balance.

METHODS

Forty-two patients were randomized: 21 continued their treatment with 4.8 g/day CaCO(3) and 21 were switched to sevelamer (initial dose: 2.4 g/day, increased to 4.4 g/day). Each month, when serum-corrected calcium decreased below 2.30 mmol/l, dialysate calcium was increased or alphacalcidol was given at each dialysis session, according to serum PO(4) levels. The following parameters were monitored: serum Ca, PO(4), bicarbonate and protein, weekly; and serum PTH, 25-OH vitamin D and total, LDL and HDL cholesterol monthly.

RESULTS

Except for higher serum phosphate at month 1, lower serum bicarbonate at month 2 and lower LDL cholesterol at month 5 in the sevelamer group, no difference was found between the two groups. Compared with baseline levels, PTH increased and 25-OH vitamin D decreased significantly in both groups, these two parameters being inversely correlated.

CONCLUSIONS

Given comparable control of plasma calcium, phosphate and 25-OH vitamin D, PTH control is comparable in both strategies. Sevelamer does not induce greater vitamin D depletion than CaCO(3). The transient decrease of serum bicarbonate after discontinuation of CaCO(3) in the sevelamer group suggests a less optimal prevention of acidosis. The sevelamer-induced decrease in LDL cholesterol gives this drug a potential advantage in cardiovascular prevention.

A toxicokinetic model for styrene and its metabolite styrene-7,8-oxide in mouse, rat and human with special emphasis on the lung

Styrene (ST) occurs ubiquitously in the environment and it is an important industrial chemical. After its uptake by the exposed mammalian organism, ST is oxidized to styrene-7,8-oxide (SO) by cytochrome P450 dependent monooxygenases. This reactive intermediate is further metabolized by epoxide hydrolase (EH) and glutathione S-transferase (GST). In long-term animal studies, ST induced lung tumors in mice but not in rats. Considering the lung to be the relevant target organ for ST induced carcinogenicity in mice, we extended a previously developed physiological toxicokinetic model in order to simulate the lung burden with ST and SO in the ST exposed mouse, rat and human. The new model describes oral and pulmonary uptake of ST, its distribution into various tissues, its exhalation and its metabolism to SO in lung and liver. It also simulates the distribution of the produced SO into the tissues and its EH and GST mediated metabolism in liver and in lung. In both organs the ST induced GSH consumption is described together with the formation of adducts to hemoglobin and to DNA of lymphocytes in ST exposed mice, rats and humans. The model includes compartments for arterial, venous and pulmonary blood, liver, muscle, fat, richly perfused tissues and lung. The latter organ is represented by two compartments, namely by the conducting and the alveolar zone. The physiological description of the pulmonary compartments relies on measured alveolar retentions, literature values of surface area of capillary endothelium, of the thickness of the tissue 'air-to-plasma', of the partition coefficient lung:blood and of metabolic parameters of ST and SO measured in pulmonary cell fractions of rodents and humans. Simulations of average pulmonary GSH levels in ST exposed rodents agree with measured data. The model predicts a significant GSH depletion (40%) in the conducting zone of mice exposed for 6 h to a ST concentration of only 20 ppm. In the conducting zone of rats, exposure to 200 ppm ST results in a loss of GSH of about 15% only. In humans, a pulmonary GSH reduction does not occur. The highest average pulmonary SO concentrations are predicted for mice, somewhat lower values for rats and by far the lowest ones for humans. Following steady state exposure to 20 ppm ST, the average SO concentration in mouse lungs is expected to be only three times higher than in rats. This difference diminishes to a factor of less than two at 70 ppm. In humans exposed to 20 ppm ST for 8 h, the average pulmonary SO burden of 0.016 micromol/kg is predicted to be about 17 and 50 times smaller than the corresponding values for rat and mouse. In agreement with reported values, pulmonary DNA adduct levels in rodents exposed to 160 ppm ST were simulated to be similar in rats and mice. In summary, there was no dramatic difference in the calculated average pulmonary SO burden between both animal species. However, pulmonary GSH loss was by far more expressed in ST exposed mice than rats. Since the model was validated on all available ST/SO data in mice, rats and humans, we consider it to be useful for estimating the risk resulting from exposure to ST.

A physiologically based pharmacokinetic model for acrylamide and its metabolite, glycidamide, in the rat

Acrylamide is a neurotoxicant and a multisite carcinogen in rats following chronic, high-dose exposures. In an effort to improve risk-based decisions for acrylamide (AMD) and its epoxide metabolite, glycidamide (GLY), a physiologically based pharmacokinetic (PBPK) model was developed for describing AMD and GLY kinetics in the rat. The PBPK model consists of components for both AMD and GLY. AMD is distributed within five compartments (arterial blood, venous blood, liver, lung, and all other tissues lumped together) and is linked to the GLY portion of the model via metabolism in the liver. GLY is distributed within the same five compartments. Dosing of AMD via the intravenous, intraperitoneal, or oral route of exposure is incorporated into the model structure. The model parameters include measured values for rat physiology (tissue volumes, blood flows), estimated tissue partition coefficients based on a published algorithm, and estimated values for metabolism and tissue binding based on fitting the model to tissue kinetic data from four studies. Despite gaps and limitations in the available database, a reliable description of the kinetics of AMD and GLY from existing studies was obtained using a single set of model parameters. The metabolism of AMD via cytochrome P-450 was best described using a Vmax of 1.6 mg/h/kg and a Km of 10 mg/L, while the metabolism of AMD via GST was described using a second-order rate constant of 0.55 L/h-mmol GSH. Similarly, the metabolism of GLY via epoxide hydrolase was best described using a Vmax of 1.9 mg/h/kg and a Km of 100 mg/L, while the metabolism of GLY via GST was described using a rate constant of 0.8 L/h-mmol GSH. These parameters were established based on the proportion of various metabolites found in urine. Future studies will need to focus on the collection of key data for refining model parameters for metabolism and tissue binding and for model validation, as well as for developing a similar model for humans. Completion of these additional studies will result in a validated rat and human PBPK model capable of predicting tissue doses linked to potential mechanisms of toxic effects for AMD and GLY and allow determination of scientifically defensible exposure limits that remain protective of human health.

Induction of micronuclei in mouse and rat by glycidamide, genotoxic metabolite of acrylamide

Male CBA mice and male Sprague-Dawley rats were treated by i.p. injection of glycidamide (GA), the presumed genotoxic metabolite of acrylamide (AA). GA was obtained through a new way of synthesis. As an endpoint of chromosome damage, micronucleus (MN) induction in erythrocytes was measured. Hemoglobin (Hb) adducts were used as a measure of in vivo dose of GA. GA induced linear dose-dependent increases in adduct levels in both species. Rats exhibit, compared with mice, 30% higher Hb adduct levels per unit of administered amount of GA. The incremental MN frequencies per administered dose of GA in mice showed a linear-quadratic dose-dependent curve. In the rat no positive dose-response relationship was obtained, probably due to toxic effects to the bone marrow. The main result of this study is the finding that after treatment with synthetic GA the MN frequency per unit of the in vivo dose of GA in the mouse is very similar to that obtained in a previous study, where animals were treated with AA and GA as a metabolite. This equality in potency of GA, whether its in vivo dose is established by injection of synthetic GA or through metabolism of AA, supports the view that GA is the predominant genotoxic factor in AA exposure.