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F Schroeder

Publications and source records attributed to F Schroeder.

At least 145 records · Page 8Linked to original sources
PubMed1987

Membrane phospholipids alter nutrient transport and drug toxicity in tumorigenic fibroblasts.

The phospholipid polar head group composition of LM cell plasma membranes was nutritionally altered by choline analogue supplementation. Phosphatidylcholine (PC), normally 60% of total phospholipid, was depleted by 60 to 90% in membranes from cells cultured with N, N'-dimethylethanolamine (DME), N-monomethylethanolamine (ME), and ethanolamine (E). Enrichment of LM cell membranes with choline analogues, such as DME-, ME-, and E-containing phospholipids, decreased the transport of [3H]thymidine, [3H]2-deoxy-D-glucose, and [14C]3-O-methylglucose. Conversely, no change in the transport of [3H] uridine or [14C]aminoisobutyric acid was observed. The toxicity of antineoplastic drugs such as 5-fluorouracil, but not daunorubicin, doxorubicin, or methotrexate, was enhanced threefold in cells enriched with phospholipid containing choline or DME as compared to ME or E. Arrhenius plots of Na+-K+-ATPase activity demonstrated a characteristic temperature at 29 degrees C in plasma membranes from choline-fed cells, while those from analogue-fed cells showed an additional break at 20 degrees C and had higher energies of activation below this temperature. In addition, choline analogue supplementation altered the protein composition of the plasma membrane. The results reported herein demonstrate that nutritional alteration of LM fibroblast plasma membrane phospholipid polar head group composition affects several transport processes and toxicity of some anticancer drugs.

Animals↗
PubMed1986

Charged anaesthetics alter LM-fibroblast plasma-membrane enzymes by selective fluidization of inner or outer membrane leaflets.

The functional consequences of the differences in lipid composition and structure between the two leaflets of the plasma membrane were investigated. Fluorescence of 1,6-diphenylhexa-1,3,5-triene(DPH), quenching, and differential polarized phase fluorimetry demonstrated selective fluidization by local anaesthetics of individual leaflets in isolated LM-cell plasma membranes. As measured by decreased limiting anisotropy of DPH fluorescence, cationic (prilocaine) and anionic (phenobarbital and pentobarbital) amphipaths preferentially fluidized the cytofacial and exofacial leaflets respectively. Unlike prilocaine, procaine, also a cation, fluidized both leaflets of these membranes equally. Pentobarbital stimulated 5'-nucleotidase between 0.1 and 5 mM and inhibited at higher concentrations, whereas phenobarbital only inhibited, at higher concentrations. Cationic drugs were ineffective. Two maxima of (Na+ + K+)-ATPase activation were obtained with both anionic drugs. Only one activation maximum was obtained with both cationic drugs. The maximum in activity below 1 mM for all four drugs clustered about a single limiting anisotropy value in the cytofacial leaflet, whereas there was no correlation between activity and limiting anisotropy in the exofacial leaflets. Therefore, although phenobarbital and pentobarbital below 1 mM fluidized the exofacial leaflet more than the cytofacial leaflet, the smaller fluidization in the cytofacial leaflet was functionally significant for (Na+ + K+)-ATPase. Mg2+-ATPase was stimulated at 1 mM-phenobarbital, unaffected by pentobarbital and slightly stimulated by both cationic drugs at concentrations fluidizing both leaflets. Thus the activity of (Na+ + K+)-ATPase was highly sensitive to selective fluidization of the leaflet containing its active site, whereas the other enzymes examined were little affected by fluidization of either leaflet.

5'-Nucleotidase↗
PubMed1986

Regulation of transbilayer distribution of a fluorescent sterol in tumor cell plasma membranes.

The lipid composition and transbilayer distribution of plasma membrane isolated from primary tumor (L-929, LM, A-9 and C3H) and nine metastatic cell lines cultured under identical conditions was examined. Cultured primary tumor and metastatic cells differed two-fold in sterol/phospholipid molar ratios. There was a direct correlation between plasma membrane anionic phospholipid (phosphatidylinositol and phosphatidylserine) content and plasma membrane sterol/phospholipid ratio. This finding may bear on the possible link between oncogenes and inositol lipids. The fluorescent sterol, dehydroergosterol, was incorporated into primary tumor and metastatic cell lines. Selective quenching of outer monolayer fluorescence by covalently linked trinitrophenyl groups demonstrated an asymmetric transbilayer distribution of sterol in the plasma membranes. The inner monolayer of the plasma membranes from both cultured primary and metastatic tumor cells was enriched in sterol as compared with the outer monolayer. Consistent with this, the inner monolayer was distinctly more rigid as determined by the limiting anisotropy of 1,6-diphenyl-1,3,5-hexatriene. Dehydroergosterol fluorescence was temperature dependent and sensitive to lateral phase separations in phosphatidylcholine vesicles and in LM cell plasma membranes. Dehydroergosterol detected phase separations near 24 degrees C in the outer monolayer and at 21 degrees C and 37 degrees C in the inner monolayer of LM plasma membranes. Yet, no change in transbilayer sterol distribution was detected in ascending or descending temperature scans between 4 and 45 degrees C. Alterations in plasma membrane phospholipid polar head group composition by choline analogues (N,N-dimethylethanolamine, N-methylethanolamine, and ethanolamine) also did not perturb transbilayer sterol asymmetry. Treatment with phenobarbital or prilocaine, drugs that selectively fluidize the outer and inner monolayer of LM plasma membranes, respectively, did not change dehydroergosterol transbilayer distribution.

Anesthetics↗
PubMed1986

Plasma membrane lipid composition modulates action of anesthetics.

The effect of LM fibroblast plasma membrane phospholipid composition on the selectivity of charged amphipathic anesthetics for exofacial or cytofacial leaflets was examined. Because preference of charged amphipaths for one of the plasma membrane bilayer leaflets may be conferred by net changes in the polar headgroup composition, LM fibroblasts were cultured in the presence of choline or N-demethylated analogs in order to change this polar headgroup composition. These altered bases were incorporated into plasma membrane phospholipids. A significant difference in 1,6-diphenyl-1,3,5-hexatriene (DPH) limiting anisotropy was observed between plasma membrane leaflets of phosphatidylcholine-, but not phosphatidylethanolamine-enriched cells. Phenobarbital, which preferentially decreased the limiting anisotropy of 1,6-diphenyl-1,3,5-hexatriene in the exofacial leaflet, had little or no preferential effect in phosphatidyl-N,N-dimethylethanolamine-enriched membranes. Prilocaine preferentially reduced the limiting anisotropy of 1,6-diphenyl-1,3,5-hexatriene in the exofacial leaflet in phosphatidyl-N-methylethanolamine-enriched membranes, exactly opposite to its effect in phosphatidylcholine-enriched membranes. In contrast, prilocaine had no selective effect in phosphatidylethanolamine-enriched membranes. In summary, the phospholipid polar headgroup composition can dramatically affect the selectivity of charged amphipathic anesthetics in altering the limiting anisotropy, a measure of restriction to motion of 1,6-diphenyl-1,3,5-hexatriene, in individual monolayers.

Anesthetics↗
PubMed1986

Dolichol alters dynamic and static properties of mouse synaptosomal plasma membranes.

Dolichols are isoprenologues that are found in almost all tissues and whose biochemical function, aside from dolichol phosphate precursors, is not known. In addition, an understanding of the organizational and dynamic properties of dolichols in biological membranes has not been forthcoming. The purpose of the experiments reported here were to examine the effects of dolichol on the physical properties of mouse synaptic plasma membranes (SPM). Differential polarized phase fluorometry indicated that dolichol both fluidized and rigidified SPM. Membrane areas detected by diphenylhexatriene and trans-parinaric acid were selectively fluidized and rigidified, respectively. It also was found that the spin label, 5-doxyl stearic acid indicated that dolichol reduced membrane fluidity. These results report for the first time a structural effect of dolichol on a biological membrane.

Animals↗
PubMed1985

Fluorescence of delta 5,7,9(11),22-ergostatetraen-3 beta-ol in micelles, sterol carrier protein complexes, and plasma membranes.

The fluorescent sterol analogue delta 5,7,9(11),22-ergostatetraen-3 beta-ol (dehydroergosterol) was synthesized and purified by reverse-phase high-performance liquid chromatography. Dehydroergosterol in aqueous solution had a critical micelle concentration of 25 nM and a maximum solubility of 1.3 microM as ascertained from fluorescence polarization and light scattering properties, respectively. Several lines of evidence indicated a close molecular interaction of dehydroergosterol with purified rat liver squalene and sterol carrier protein (SCP). SCP increased the maximal solubility of dehydroergosterol in aqueous buffer. The fluorescence emission spectrum of dehydroergosterol was blue shifted upon addition of SCP. The fluorescence lifetime of dehydroergosterol in aqueous buffer was 2.3 ns; addition of SCP resulted in the appearance of a second lifetime component near 12.4 ns. The SCP increased the fluorescence polarization of monomeric dehydroergosterol in aqueous buffer from 0.033 to 0.086. Scatchard analysis of the binding data indicated that dehydroergosterol interacted with purified rat liver SCP with an apparent KD = 0.88 microM and Bmax = 4.8 microM. At maximal binding, 1.0 mol of dehydroergosterol was specifically bound per mole of SCP. The close molecular interaction of dehydroergosterol with SCP was also demonstrated by energy-transfer experiments. The intermolecular distance between SCP and bound dehydroergosterol was evaluated by fluorescence energy transfer from tyrosine residues of SCP to the conjugated triene series of double bonds in dehydroergosterol. The transfer efficiency was 36%, and R, the apparent distance between the tyrosine energy donor and the dehydroergosterol energy acceptor, was 19 A. The significance of these data obtained in vitro for dehydroergosterol interaction with SCP was also tested in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Sterol and squalene carrier protein interactions with fluorescent delta 5,7,9(11)-cholestatrien-3 beta-ol.

The fluorescent sterol delta 5,7,9(11)-cholestatrien-3 beta-ol (cholestatrienol) was used as an analogue of cholesterol to determine the properties of the sterol in aqueous buffer and the interaction of cholesterol with sterol and squalene carrier protein (SCP). Cholestatrienol was synthesized and purified to a stable product by reverse phase high performance liquid chromatography. The critical micelle concentration of cholestatrienol in aqueous buffer was 1 nM while its maximum solubility was 1.15 microM as ascertained from fluorescence polarization and light scattering properties, respectively. Several lines of evidence indicated a close molecular interaction of cholestatrienol with purified rat liver SCP. The fluorescence emission spectrum of monomeric cholestatrienol in aqueous buffer was blue shifted upon addition of SCP. The fluorescence lifetime of monomeric cholestatrienol in aqueous buffer was increased by SCP from 5 to 12 ns. The SCP increased the fluorescence polarization of monomeric cholestatrienol from 0.002 to 0.38 in aqueous buffer. The close molecular interaction of cholestatrienol with SCP was also demonstrated by energy transfer experiments. Fluorescence energy transfer from tyrosine residues of SCP to the conjugated triene fluorophore in cholestatrienol had a transfer efficiency of 59%. R, the apparent distance between the tyrosine energy donor and the cholestatrienol energy acceptor, was 16.3 A. Binding analysis indicated that cholestatrienol interacted with SCP with an apparent KD = 0.5 microM and a Bmax = 3.54 microM. One mol of cholestatrienol was bound per mol of SCP. These results demonstrate the utility of cholestatrienol not only as a membrane sterol probe molecule but also as a probe for sterol-protein interactions.

Animals↗
PubMed1985

Roles of proton removal and membrane fluidity in Na+- and Cl(-)-dependent uptake of gamma-aminobutyric acid by mouse brain particles.

Proton removal is required for Na+-dependent uptake of GABA into mouse brain microsomal particles (P3) to take place at 0 degrees C and pH 7.3. No temporal coordination was demonstrated to exist between proton removal and GABA uptake processes, ruling out the possibilities that either a proton gradient or proton outflux from the particles is required. Observations on proton dissociation from the particles indicated that the protons are derived from a particulate compartment that is not in pH equilibrium with the bulk solution. Experiments on the effects of temperature on GABA uptake in the presence of 80 mM NaCl alone or with 10 mM triethanolamine (TREA) at pH 7.3 showed that the effects of TREA and temperature were interactive. The relative enhancing effects of TREA on GABA uptake diminished progressively with increasing temperature. The break points in Arrhenius plots obtained in presence and absence of TREA were the same, indicating that the effect of TREA was not on bulk viscosity of the membrane. Measurements made of fluorescence polarization as a function of temperature and of the absorbance-corrected fluorescence using TMA-DPH, a probe believed to be anchored at the lipid-water interface, showed clearly that the characteristic viscosity changes that take place with temperature in the membrane regions through which the probe is distributed were not correlated with the effects of temperature on GABA uptake. It is tentatively concluded that the protons may be attached to the membranes of the P3 particles by strong coulombic interactions in unstirred electrical double layers, possibly both on the inside and outside of particles. The importance of the existence of differences between pH at the surfaces of membranes, possibly both on the inside and outside of the particles, and that of the bulk solutions that bathe them was reiterated.

Animals↗
PubMed1984

Correlation of tumor metastasis with sterol carrier protein and plasma membrane sterol levels.

Squalene and sterol carrier protein (SCP) levels and sterol/phospholipid molar ratios of whole cells and plasma membranes were measured in cultured primary tumor and metastatic cell lines. SCP is abundant in all cell lines. However, metastatic lines have significantly lower SCP levels and plasma membrane sterol/phospholipid ratios than do primary lines. The results indicate that extremely malignant, metastatic cells are unable to produce or maintain adequate levels of both SCP and plasma membrane sterols when grown in lipoprotein deficient media. This defect, in vivo, probably causes excess uptake of SCP and lipid.

Animals↗
PubMed1984

Fluorescence probes in metastatic B16 melanoma membranes.

Fluorescence probe molecules, trans-parinaric acid and 1,6-diphenylhexatriene, were utilized to characterize the structure of plasma membranes, microsomes and mitochondria from B16 melanoma cells. High metastastic B16-F10 and low metastatic B16-F1 melanoma cell lines had markedly different membrane structures. The fluorescence polarization, fluorescence lifetime and limiting anisotropy of trans-parinaric acid were significantly lower (P less than 0.05) in all three membrane fractions of the B16-F1 cell line than in the corresponding membranes of the B16-F10 cell line. These data indicated less restriction to rotational motion in the solid lipid domains of B16-F1 cell membranes preferentially sensed by trans-parinaric acid. The limiting anisotropy of both trans-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene was significantly lower in the outer monolayer than the inner monolayer of the plasma membrane of B16-F1 cells but not in B16-F10 cells. A breakpoint in Arrhenius plots of fluorescence near 30-34 degrees C indicated the presence of a phase separation that was assigned to the inner monolayer of the plasma membrane. However, no differences in this breakpoint temperature were noted between the B16-F1 and B16-F10 melanoma membranes. Thus, more fluid solid membrane domains and a distinct transbilayer fluidity difference were characteristic of plasma membranes from low metastatic B16-F1 melanoma cells in contrast to high metastatic B16-F10 melanoma cells.

Animals↗
PubMed1984

Sex and age alter plasma membranes of cultured fibroblasts.

Human skin fibroblasts were taken from age-matched male and female subjects. The cells were then cultured under identical conditions and passage-number matched. Plasma membranes were isolated and membrane enzyme activities, lipid composition, and structure of isolated plasma membranes were measured in order to determine the presence of significant sex differences in human fibroblast membrane properties. The results indicated that plasma membranes from normal female subjects had a 1.6-fold and 3.6-fold higher cholesterol/phospholipid ratio and oleic acid (18:2) content than normal male subjects. The limiting anisotropy and the rotational relaxation time of fluorescence probe molecules such as trans-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene in the plasma membranes was not significantly different from fibroblasts of male versus female normal subjects. The total activity of plasma membrane (Na+, K+)-ATPase was significantly higher in female than male normal subjects. A potential 'membrane structural disorder', Huntington's disease, was confirmed in fibroblast membranes from male but not from female Huntington's disease subjects. The possibility that Huntington's disease was a 'premature membrane aging' phenomenon was considered. A comparison of plasma membrane enzymes, lipids, and structure from old and young Huntington's disease subjects did not show differences consistent with accelerated membrane aging as explaining the molecular basis for the disease. The age-dependent differences noted in aged Huntington's disease subjects: increased phosphatidylcholine/phosphatidylethanolamine ratio and sphingomyelin + lysophosphatidylcholine content of fibroblast plasma membranes were not significantly altered when compared to normal age-matched controls. However, (Na+, K+)-ATPase activity was significantly enhanced in fibroblast plasma membranes of older Huntington's disease subjects unlike those of control subjects. In conclusion, sex and age differences in membrane properties of cultured cells represent important potential variables in the elucidation of human genetic disorders that may be membrane-related.

Adult↗
PubMed1984

delta 5,7,9(11)-Cholestatrien-3 beta-ol: a fluorescent cholesterol analogue.

Structural analysis, a purification scheme and stability information on a fluorescent cholesterol analogue, which has been used as a probe in several model and biological systems, are presented. The proposed structure for the fluorophore, cholestatrien-3 beta-ol, closely resembles that of cholesterol. However, problems of low yield during synthesis and rapid decomposition have impeded its use. This study concerns the synthesis and purification of cholestatrien-3 beta-ol by reverse phase high performance liquid chromatography (HPLC). Unlike cholestatrien-3 beta-ol recrystallized from solvents, the fluorescent sterol purified by HPLC was stable over several months at -70 degrees C either as a white, crystalline powder or in ethanolic solution. In model membranes the fluorescence of cholestatrien-3 beta-ol was stable to ultraviolet (UV) light. A simple spectroscopic assay for purity is presented. Included are detailed absorbance, fluorescence, mass, 1H-NMR, and 13C-NMR spectral analyses. The data confirm the structure of cholestatrien-3 beta-ol proposed, but not proven, over 50 years ago, delta 5,7,9(11)-cholestatrien-3 beta-ol.

Cholestenes↗
PubMed1984

2-hexanone potentiation of [14C]chloroform hepatotoxicity: covalent interaction of a reactive intermediate with rat liver phospholipid.

Rats were treated with [14C]chloroform (14CHCl3) in corn oil (CO) or corn oil alone 18 hr following pretreatment with 2-hexanone (2-HX) in corn oil or corn oil alone. Livers were removed, homogenized 1,2, and 6 hr post-14CHCl3 administration, and glutathione (GSH) content, irreversible binding of 14CHCl3-derived radiolabel, and phospholipid composition were determined. The combination of 2-HX + CHCl3 reduced GSH content to 21% of control (CO + CO) 1 hr after CHCl3 administration. No significant rebound of GSH was observed 24 hr post-CHCl3 administration. In contrast, GSH was not altered by administration of CHCl3 to CO-pretreated rats. Although 14CHCl3-derived radiolabel was irreversibly bound to hepatic macromolecules of both CO- and 2-HX-pretreated rats, total irreversibly bound 14C was significantly enhanced in 2-HX-pretreated rats at all time points. The latter observation was consistent with the decrease in GSH of 2-HX-pretreated rats. Total 14C binding in 2-HX-pretreated rats reached a plateau 2 hr post-14CHCl3 administration and was distributed 52% in protein, 41% in lipid, and 7% in acid soluble fractions 6 hr post-14CHCl3 administration. 2-HX enhanced 14C binding to protein and lipid at each time point. Radiolabel was not detected in neutral lipids of control or 2-hexanone-treated animals, but was enhanced 33-fold in phospholipids of 2-hexanone-treated animals. Phospholipid fatty acid methyl ester derivatives did not contain 14C indicating the radiolabel was most likely associated with phospholipid polar head groups. Two dimensional thin layer chromatographic analysis of phospholipid from treated animals demonstrated that 87% of the total radiolabel was associated with a specific phospholipid (14C-PL) which had a 1:1 molar ratio of phosphate to 14C. The latter indicates that the 14C-PL was a monophospholipid derivative of 14CHCl3 reactive intermediate, generally thought to be phosgene. Concurrent decrease in phosphatidylethanolamine content from 23% of total phospholipid to 7%, accumulation of 14C-PL to 2.6% of total phospholipid, and increase in lysophosphatidylethanolamine from 1 to 7% of total phospholipid during 2-hexanone + 14CHCl3 treatment indicated that the amine moiety of phosphatidylethanolamine polar head groups was the probable target of phosgene-lipid interaction, and that a degradative pathway existed which removed the abnormal phospholipid from hepatic membranes. No phospholipid other than phosphatidylethanolamine was depleted. During models studies, 2% phosgene in toluene was reacted with liver phosphatidylethanolamine for 6 hr at 37 degrees C.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Age-related alterations in cultured human fibroblast membrane structure and function.

Membrane enzyme activities, lipid composition, and fluorescence probe characteristics in isolated plasma membranes, microsomes and mitochondria of cultured human fibroblasts were used to determine if structural alterations occurred as a function of donor age. The cells were sex matched and allowed to undergo approximately 8 population doublings under identical culture conditions. Plasma membrane (Na+, K+)-ATPase, microsomal NADPH cytochrome c reductase, and mitochondrial succinate cytochrome c activities showed variation as a function of increasing donor age but these changes were not statistically significant. At the same time the cholesterol/phospholipid molar ratio was unaltered in plasma membranes, decreased 50% in microsomes, and unchanged in mitochondria with increasing donor age. The phosphatidylcholine/phosphatidylethanolamine ratio increased in all three membrane fractions with increasing age of the fibroblast donor. The ratio of unsaturated/saturated fatty acids decreased in the phospholipids of microsomes but not of plasma membranes or mitochondria. The structural properties of the membranes were determined with two different fluorescence probe molecules, trans-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene. These probe molecules indicated that the fluorescence lifetime and/or fluorescence polarization of the trans-parinaric acid probe decreased in microsomes, mitochondria, and in the plasma membrane, such that the limiting anisotropy, indicative of restrictions to probe motions, was significantly lower (high fluidity) with increasing subject age in plasma membranes, microsomes and mitochondria. The trans-parinaric acid fluorescence lifetime displayed two components in plasma membranes, microsomes, and mitochondria, a finding consistent with the coexistence of fluid and solid membrane lipid areas in the cultured human fibroblast subcellular membranes. The trans-parinaric acid partitioned preferentially into solid membrane areas. The limiting anisotropy of 1,6-diphenyl-1,3,5-hexatriene, a fluorescent probe that partitioned almost equally into different lipid domains, was also decreased in microsomes and mitochondria with increasing donor age. In contrast, 1,6-diphenyl-1,3,5-hexatriene indicated a small increase in limiting anisotropy (0.219 vs 0.195) in plasma membranes. Arrhenius plots of trans-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene absorbance-corrected fluorescence in plasma membranes, microsomes and mitochondria demonstrated characteristic breakpoints near 20 degrees C and 30 degrees C. These breakpoints were not altered as a function of age.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1984

Role of membrane lipid asymmetry in aging.

Recent advances in our understanding of the asymmetric distribution of lipids across nervous system membranes coupled with the application of biophysical techniques to examine transbilayer structure and function have led to the formulation of a new hypothesis. The author hopes that the insights presented herein will stimulate investigation into this developing new field. The theory provides an approach to correlation the accumulation of nervous tissue membrane peroxidative and cross-linking damage, the loss of transbilayer lipid asymmetry, and loss of transbilayer neuroendocrine, transport, secretory and immunoregulatory functions. Central to this scheme is the role of membrane lipid asymmetry in regulation to and/or coupling of transbilayer functions.

Aging↗
PubMed1984

Mechanisms in 2-hexanone potentiation of chloroform hepatotoxicity.

2-Hexanone (2-Hx) is known to potentiate chloroform (CHCl3) hepatotoxicity in part by increasing the bioactivation of CHCl3 to phosgene (COCl2). Treatment of rats with 2-Hx + CHCl3 in vivo did not initiate peroxidation of hepatic fatty acids as determined by formation of conjugated dienes or depletion of unsaturated fatty acids, or as determined by production of malondialdehyde (MDA) in vitro. A 5-fold decrease in the specific activity of succinate-dependent cytochrome c reductase in liver from rats treated in vivo with corn oil (vehicle) + CHCl3 and in rats treated with 2-Hx + CHCl3 indicated that a mechanism independent of CHCl3 bioactivation may add to the hepatotoxic effects which result from the metabolism of chloroform to phosgene.

Animals↗