One- and two-dimensional NMR relaxation studies of dynamics and structure in bile salt-phosphatidylcholine mixed micelles

Quantitative Analysis of Apoptotic Cell Death Using Proton Nuclear Magnetic Resonance Spectroscopy

Quantification of apoptotic cell death in vivo has become an important area of investigation in patients with acute lymphoblastic leukemia (ALL). We have devised a noninvasive analytical method to estimate the percentage of apoptotic lymphoblasts in doxorubicin-treated Jurkat T-cell ALL cultures, using proton nuclear magnetic resonance spectroscopy (1H NMR). We have found that the ratio of the methylene (CH2 ) resonance (at 1.3 ppm) to the methyl (CH3 ) resonance (at 0.9 ppm) signal intensity, as observed by 1H NMR, is directly proportional to the percentage of apoptotic lymphoblasts in vitro. The correlation between the CH2/CH3 signal intensity ratio and the percentage of apoptotic lymphoblasts was optimal 24 to 28 hours after doxorubicin treatment (r2 = .947, N = 27 samples). There was also a direct temporal relationship between an increase in the CH2/CH3 signal intensity ratio and the onset of apoptosis as detected by nuclear morphologic analysis, fluorescein-annexin V flow cytometry, and DNA gel electrophoresis. Thin-layer chromatography confirmed that a dynamic and/or compositional change of the plasma membrane, rather than increases in lipase activity or fatty acid production, appears to account for the increase in the CH2/CH3 signal intensity ratio during apoptosis. 1H NMR may have clinical utility for the early noninvasive assessment of chemotherapeutic efficacy in patients with ALL.

Quantitative Analysis of Apoptotic Cell Death Using Proton Nuclear Magnetic Resonance Spectroscopy

Quantification of apoptotic cell death in vivo has become an important area of investigation in patients with acute lymphoblastic leukemia (ALL). We have devised a noninvasive analytical method to estimate the percentage of apoptotic lymphoblasts in doxorubicin-treated Jurkat T-cell ALL cultures, using proton nuclear magnetic resonance spectroscopy (1H NMR). We have found that the ratio of the methylene (CH2 ) resonance (at 1.3 ppm) to the methyl (CH3 ) resonance (at 0.9 ppm) signal intensity, as observed by 1H NMR, is directly proportional to the percentage of apoptotic lymphoblasts in vitro. The correlation between the CH2/CH3 signal intensity ratio and the percentage of apoptotic lymphoblasts was optimal 24 to 28 hours after doxorubicin treatment (r2 = .947, N = 27 samples). There was also a direct temporal relationship between an increase in the CH2/CH3 signal intensity ratio and the onset of apoptosis as detected by nuclear morphologic analysis, fluorescein-annexin V flow cytometry, and DNA gel electrophoresis. Thin-layer chromatography confirmed that a dynamic and/or compositional change of the plasma membrane, rather than increases in lipase activity or fatty acid production, appears to account for the increase in the CH2/CH3 signal intensity ratio during apoptosis. 1H NMR may have clinical utility for the early noninvasive assessment of chemotherapeutic efficacy in patients with ALL.

The conformational properties of the antineoplastic ether lipid 1-thiohexadecyl-2-O-methyl-S-glycero-3-phosphocholine

Thio analogs of platelet activating factor (PAF) are of great interest because they exhibit antineoplastic properties both in vitro and in vivo. In contrast to most known anticancer agents, these lipids appear not to act through the synthesis and function of DNA and, therefore, offer a new avenue of approaching cancer chemotherapy. We have examined the conformational properties of 1-thiohexadecyl-2-O-methyl-S-glycero-3-phosphocholine (ET-S-16-OCH3) in organic solvents and in micelles. The conformational analysis was based on a combination of 1D, 2D NMR spectroscopy and molecular graphics. 1H and 13C spin lattice relaxation time (T1) experiments were also performed to study the dynamic properties of this molecule. The picture emerging from these studies is as follows. The alkyl chain of ET-S-16-OCH3 is the most mobile part of the molecule both in CDCl3/CD3OD and in micelles and exists as a mixture of interconverting conformers including an extended all trans and several low energy conformers with one or more gauche segments. This creates a twisting of the chain and facilitates a spatial communication between the alkyl chain and the glycerol backbone as well as between the alkyl chain and the headgroup. The methylene groups of the thioglycerol backbone and the headgroup are the least mobile while the methine group of the thioglycerol backbone appears to have an intermediate mobility. The conformation of the thioether lipid in the two media may be of relevance during its interaction with its site of action, the cellular membrane. Such a conformation may also play an important role in determining the selectivity of this interaction with different cell membranes.

Diffusivity of bile salt/phospholipid aggregates in mucin

PURPOSE

The objective of this study is to evaluate the effect of the mucous layer on the transport of the drug-solubilizing bile salt/phosphatidylcholine (BS/PC) aggregates.

METHODS

The self-diffusion coefficient of BS/PC aggregates in bovine submaxillary mucin (BSM) was measured by Fourier-transform pulsed-field gradient spin-echo (FT-PGSE) 1H NMR spectroscopy.

RESULTS

In spite of the complexity of the mixture, the FT-PGSE technique allowed the unambiguous determination of the diffusivity of PC and 1H2HO (HDO, natural abundance in D2O). With a series of BS/PC total lipid concentrations ranging from 1 to 7 g/dl, a progressive decrease in the effective diffusivity of HDO was observed with an increase in the both the BSM and total lipid concentration. The effective diffusivity of PC decreased with increasing lipid concentrations in the presence of mucin, while in the controls it increased. After correcting the effective diffusivity of PC for the obstruction effect of mucin, the size of the BS/PC mixed micelle was assessed. It appears that PC associates with BSM resulting in a decrease in the available PC for micellization. This reduces the average size of the mixed micelle within the mucous layer.

CONCLUSIONS

The aggregation state of BS/PC micelle is altered by the presence of mucin which would have a direct impact on the transport of dietary lipid and solubilized drug through the aqueous boundary layer of the intestinal tract.

Physicochemical and physiological properties of cholylsarcosine. A potential replacement detergent for bile acid deficiency states in the small intestine

The properties of cholylsarcosine (the synthetic N-acyl conjugate of cholic acid with sarcosine [N-methylglycine]) were examined to determine its suitability as a bile acid replacement agent for conditions of bile acid deficiency in the small intestine, which causes fat malabsorption. Previous studies in rodents had shown that the compound was well transported by the liver and ileum and underwent neither deconjugation nor dehydroxylation during enterohepatic cycling. By 1H-nuclear magnetic resonance, cholylsarcosine was found to exist in dilute aqueous solution as an almost equimolar mixture of two geometric isomers--cis and trans (around the amide bond)--in contrast to cholylglycine, which was present entirely in the trans form. The critical micellization concentration was 11 mmol/liter, similar to that of cholylglycine (10 mmol/liter). By nonaqueous titrimetry, the pKa' of cholylsarcosine was 3.7, only slightly lower than that of cholylglycine (3.9). Cholylsarcosine was poorly soluble below pH 3.7, but highly soluble above pH 4. In vitro, cholylsarcosine behaved as cholylglycine with respect to promoting lipolysis by lipase/colipase. There was little difference between cholylsarcosine and cholylglycine in their solubilization of an equimolar mixture of oleic acid, oleate, and monoolein (designed to simulate digestive products of triglyceride) or in their solubilization of monooleyl-glycerol alone. When a [3H]triolein emulsion with either cholylsarcosine or cholyltaurine was infused intraduodenally in biliary fistula rats, recovery of 3H in lymph was 52 +/- 10% (mean +/- SD) for cholylsarcosine and 52 +/- 11% for cholyltaurine. When perfused into the colon of the anesthetized rabbit, cholylsarcosine (5 mmol/liter) did not influence water absorption or permeability to erythritol, in contrast to chenodeoxycholate, which induced vigorous water secretion and caused erythritol loss. We conclude that cholylsarcosine possesses the physicochemical and physiological properties required for a suitable bile acid replacement in deficiency states.

Magic-angle spinning NMR studies of molecular organization in multibilayers formed by 1-octadecanoyl-2-decanoyl-sn-glycero-3-phosphocholine

Magic-angle spinning 1H and 13C nuclear magnetic resonance (NMR) have been employed to study 50%-by-weight aqueous dispersions of 1-octadecanoyl-2-decanoyl-sn-glycero-3-phosphocholine (C[18]:C[10]PC) and 1-octadecanoyl-2-d19-decanoyl-PC (C[18]:C[10]PC-d19), mixed-chain phospholipids which can form interdigitated multibilayers. The 1H NMR linewidth for methyl protons of the choline headgroup has been used to monitor the liquid crystalline-to-gel (LC-to-G) phase transition and confirm variations between freezing and melting temperatures. Both 1H and 13C spin-lattice relaxation times indicate unusual restrictions on segmental reorientation at megahertz frequencies for C(18):C(10)PC as compared with symmetric-chain species in the LC state; nevertheless each chemical moiety of the mixed-chain phospholipid exhibits motional behavior that may be classified as liquidlike. Two-dimensional nuclear Overhauser spectroscopy (NOESY) on C(18):C(10)PC and C(18):C(10)PC-d19 reveals cross-peaks between the omega-methyl protons of the C18 chain and the N-methyl protons of the phosphocholine headgroup, and several experimental and theoretical considerations argue against an interpretation based on spin diffusion. Using NMR relaxation times and NOESY connectivities along with a computational formalism for four-spin systems (Keepers, J. W., and T. L. James. 1984. J. Magn. Reson. 57:404-426), an estimate of 3.5 A is obtained for the average distance between the omega-methyl protons of the C18 chain and the N-methyl protons of the phosphocholine headgroup. This finding is consistent with a degree of interdigitation similar to that proposed for organized assemblies of gel-state phosphatidylcholine molecules with widely disparate acyl-chain lengths (Hui, S. W., and C.-H. Huang. 1986. Biochemistry. 25:1330-1335); however, acyl-chain bendback or other intermolecular interactions may also contribute to the NOESY results. For multibilayers of C(18):C(10)PC in the gel phase, 13C chemical-shift measurements indicate that trans conformers predominate along both acyl chains. 13C Spin-lattice relaxation times confirm the unusual motional restrictions noted in the LC state; nevertheless, 13C and 1H rotating-frame relaxation times indicate that the interdigitated arrangement enhances chain or bilayer motions which occur at mid-kilohertz frequencies.

Liposomes prepared dynamically by interactions between bile salt and phospholipid molecules

Quasi-elastic light scattering (QELS) studies showed that vesicles can spontaneously form from sodium glycocholate-egg phosphatidylcholine mixed micelles upon dilution with physiological saline buffer (pH 7.5). A water-soluble drug, cytosine arabinoside, did not affect the transition pattern. Transitions were also obtained when dilutions were performed using diluted serum solutions (5% and 10% serum in buffer). However, if intermicellar bile salt monomer concentration (imc) was kept constant in diluent media, the transition was completely suppressed. Approximately 10% of the cytosine arabinoside was trapped inside vesicles which were formed in buffer, although this value decreased to approx. 2.5% when diluted serum was used. These results suggest that the mixed micelle to vesicle transition can be an alternative means to sonication in loading drugs into in vitro vesicles. A good correlation was found between the transmission electron microscopy (TEM) diameter and the mean hydrodynamic diameter obtained by QELS.

NMR studies of backbone-alkylated DNA: duplex stability, absolute stereochemistry, and chemical shift anomalies of prototypal isopropyl phosphotriester modified octanucleotides, (Rp,Rp)- and (Sp,Sp)-(d-[GGA(iPr)ATTCC])2 and -(d-[GGAA(iPr)TTCC])2

The DNA octamer (d-[GGAATTCC])2 and four alkylated analogues, (Rp)-(d-[GGA(iPr)ATTCC])2, (Sp)-(d-[GGA(iPr)ATTCC])2, (Rp)-(d-[GGAA(iPr)TTCC])2, and (Sp)-(d-[GGAA(iPr)TTCC])2 have been examined using 1H and 31PNMR spectroscopies. Duplex stability, as monitored by both NMR and optical measurements, is shown to be a function of both site and stereochemistry of the phosphotriester moiety. Chemical shift changes relative to the native octamer indicate that there are long-range perturbations in the isopropylated molecules. 1HNMR is shown to be a general means by which stereochemistry at phosphorous can be determined.