O. Kucuk

Diet and stomach cancer incidence : a case-control study in Turkey

A case‐control study of diet and stomach cancer was conducted in Ankara, Turkey, between December 1987 and March 1988. One hundred patients with adenocarcinoma of the stomach were matched with 100 control subjects according to age, sex, and residential area. A dietary questionnaire was administered to all subjects by one of the authors. Gastric cancer patients consumed less fresh fruit and yellow‐green vegetables (P < 0.0001) and meats (P < 0.001), and more salted food (P < 0.001), condiments (P < 0.0001), and salt (P < 0.001) compared with the control group. Twenty‐four percent of the gastric cancer patients and 4% of the controls had no refrigerator (P < 0.0001). There was no difference between the two groups with regard to the consumption of starches, fried foods, cereals, milk, dairy products, tea, alcohol, and tobacco. Stomach cancer patients brushed their teeth less frequently (P < 0.0001) and had more deficient teeth (P < 0.0001) compared with the control group.

The effects of cholesterol oxidation products in sickle and normal red blood cell membranes

The oxysterol content in normal and sickle red blood cell (RBC) membranes was assessed using thin-layer chromatography and capillary gas chromatography/mass spectrometry. Several more oxysterols were present in sickle RBCs compared to normal RBCs. Sickle RBC membranes had a higher concentration of 5 alpha,6 alpha-epoxycholesterol, 5 alpha-cholestane-3 beta,5,6 beta-triol, 7-ketocholesterol and 19-hydroxycholesterol than normal RBC membranes. The increased oxysterols in sickle RBC may be an effect of the increased oxidative stress which occurs in sickle RBC membranes. Physical characteristics of normal and sickle RBC membrane ghosts with and without inserted oxysterols were examined by Fourier transform infrared spectroscopy. The data are consistent with a greater sterol content in sickle cells compared to normal RBC membranes, and a possible oxysterol-cholesterol synergism.

Inhibition of NK cell-mediated cytotoxicity by oxysterols.

Some of the oxidation products of cholesterol (oxysterols) have profound effects on plasma membrane structure and function. The present studies were undertaken to determine the effects of oxysterols on NK cell-mediated cytotoxicity. When mouse spleen cells were preincubated with certain oxysterols, NK cell cytotoxicity was inhibited without loss of effector cell viability. The strongest inhibition was observed with oxysterols that are oxidized at the C-5, C-6, or C-7 positions of the sterol nucleus. Among these, 7 beta-hydroxycholesterol caused more inhibition than 7 alpha-hydroxycholesterol suggesting that the spatial orientation of the hydroxyl group in the beta-position results in a greater perturbation in plasma membrane structure than that oriented in the alpha-position. In contrast, oxysterols that are oxidized at the C-20 and C-25 positions that are located on the C-17 acyl chain had little or no inhibitory effect, suggesting that oxidation in the cholesterol nucleus which is situated closer to the phospholipid headgroups at the lipid bilayer-aqueous interface results in a more profound effect on the plasma membrane physical structure. These results suggest that the lytic function of NK cell is sensitive to alterations in the physical state of its plasma membrane induced by oxysterols.

The effect of intensive intermittent maintenance therapy in advanced low-grade non-Hodgkin's lymphoma

One hundred and eleven patients with low‐grade histology non‐Hodgkins lymphoma achieving a restaged complete response to one of three induction therapies on Eastern Cooperative Oncology Group (ECOG) protocol EST 2474 were randomized to receive either maintenance treatment with BCNU, cyclophosphamide, vincristine, and prednisone (BCVP) given every 6 weeks for an additional 18 months or no further therapy. Overall toxicity was moderate. The median progression‐free survival (PFS) on maintenance therapy was 3.2 years versus 2.0 years for those observed without treatment (P = 0.02). Progression‐free survival was significantly shorter for patients with nodular and diffuse pattern (ND), histiocytic or mixed histology compared with pure nodular lymphocytic, or poorly differentiated counterpart (P = 0.0007), thus confirming the prognostic significance of histologic subtypes. However, the overall survival of patients was not improved by maintenance treatment, suggesting that therapy upon relapse was an equally effective alternative clinical strategy.

The influence of oxygenated sterol compounds on dipalmitoylphosphatidylcholine bilayer structure and packing

Fourier Transform Infra-red and Raman Spectroscopies indicate that 7 alpha-hydroxycholesterol and 7-ketocholesterol have a diminished capacity to condense (increase the packing order of) fluid-state dipalmitoylphosphatidylcholine (DPPC) acyl chains when compared with the effects of cholesterol and the other oxidized sterols studied. DPPC head groups were also more ordered by 7-ketocholesterol over the temperature range 10 degrees - 70 degrees C. Primary effects of these sterols appear to be associated with the hydrophillic regions of the DPPC bilayer, although packing arrangements with acyl chains are also involved. Phosphate and acyl chain ester groups were observed to possess a packing order which was invariant which indicates that these may be the target groups in the interaction with 7-ketocholesterol. A surprising observation was the synergistic amplification of the effects of 7-ketocholesterol by the presence of cholesterol in the DPPC bilayer.

Oxygenated cholesterols synergistically immobilize acyl chains and enhance protein helical structure in human erythrocyte membranes

Fourier transform infrared spectroscopy revealed that insertion of 20 alpha-hydroxycholesterol into human erythrocyte membranes (10% of total membrane sterol) immobilized the lipid acyl chains to a degree equivalent to enriching total membrane cholesterol by 50% (Rooney, M.W., Lange, Y. and Kauffman, J.W. (1984) J. Biol. Chem. 259, 8281-8285). Raman spectroscopy showed that the amount of acyl chain rotamers was not significantly altered by the presence of 20 alpha-hydroxycholesterol, indicating that acyl chain immobilization was limited to an inhibition of lateral motion. The presence of 20 alpha-hydroxycholesterol may synergistically enhance the acyl-chain-immobilizing behavior of membrane cholesterol. In addition, protein helical structure was not altered by 20 alpha-hydroxycholesterol. The insertion of 7 alpha-hydroxycholesterol into erythrocyte membranes resulted in an increase in protein helical structure which was comparable to that observed for erythrocyte membranes enriched with pure cholesterol by 50%. However, both acyl chain mobility and conformation were unchanged. These results suggest a synergistic behavior between oxysterols and cholesterol in modifying erythrocyte membrane packing.

Inhibition of cytolytic T lymphocyte activity by oxysterols

The objective of this study was to investigate the effects of oxysterols (OS), namely 5α-hydroxy-6-ketocholestanol, 6-ketocholestanol and 25-hydroxycholesterol, on specific cell-mediated cytotoxicity by C57BL/6 spleen cells against P815-X2 (a DBA/2 mastocytoma) target cells. Cytolytic T lymphocytes (CTL) were generated by intraperitoneally injecting C57BL/6 mice with P815-X2 tumor cells 10 d prior to the cytotoxicity experiments. Preincubation of CTL with 10−5 M 5α-hydroxy-6-ketocholestanol and 6-ketocholestanol for 45 min in lipoprotein-depleted medium resulted in an inhibition of cytolytic activity (73 and 43%, respectively) as measured by 4-h51Cr release. At a concentration of 5×10−6 M, 5α-hydroxy-6-ketocholestanol inhibited CTL activity by 65%, whereas 6-ketocholestanol did not elicit any inhibition. By contrast, 25-hydroxycholesterol did not inhibit CTL at either concentration, although it is known to be a potent inhibitor of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway. When CTL were preincubated with OS in lipoprotein-replete medium, there was no inhibition of CTL activity at the respective concentrations. The results suggest that the inhibition of CTL activity upon short-term incubation with OS is not due to the inhibition of cholesterol synthesis, but may be due to the insertion of OS into the plasma membrane to replace cholesterol and alteration of membrane physical properties.

Sterols stabilize the ripple phase structure in dihexadecylphosphatidylcholine

The presence of various sterols in mixtures with dihexadecylphosphatidylcholine (DHPC) was studied using static X-ray diffraction of temperature equilibrated samples, and real-time X-ray diffraction of samples undergoing temperature scans. It was found that these sterols eliminate the interdigitation of the alkyl chains in the DHPC sub-gel and gel-state bilayers while stabilizing the ripple gel-state at the expense of the gel-state bilayer phase. The ripple-ripple phase transition previously observed for dipalmitoylphosphatidylcholine in the presence of low molar concentrations of sterols (Wolfe et al. (1992) Phys. Rev. Lett. 68, 1085-1088) was also observed for similar DHPC-sterol mixtures. In addition, we show the first evidence that the presence of 5 alpha-cholestane-3 beta,5,6 beta-triol will cause the lipid mixtures to continue to adopt a ripple mesophase structure even after the DHPC alkyl chain becomes disordered.

Lower extremity vasospasm associated with ischemic neuropathy, dermal fibrosis, and digital gangrene in a patient with carcinoid syndrome

Bilateral lower extremity vasospasm associated with severe pain and hyperesthesias in the legs, and digital gangrene in both feet developed in a 50‐year‐old man with carcinoid syndrome. Nifedipine and chemical lumbar sympathectomy were partially effective in relieving the vasospasm. Electromyographic findings were consistent with ischemic neuropathy. A skin biopsy specimen showed striking dermal fibrosis. Serotonin and other vasoconstrictor substances released from the tumor may be responsible for the vasospasm, the dermal sclerosis, and the ischemic neuropathy. The early use of lumbar sympathectomy in patients with lower extremity vasospasm may prevent these irreversible ischemic complications.

Real-time X-ray diffraction study at different scan rates of phase transitions for dipalmitoylphosphatidylcholine in KSCN

Multibilayer arrays of dipalmitoylphosphatidylcholine (DPPC) in 1 M KSCN were characterized using real-time X-ray diffraction and differential scanning calorimetry. A phase transition sequence was observed as a function of increasing temperature which involved changes from the interdigitated subgel (Lc(inter)) to interdigitated gel (L beta(inter)) to disordered (L alpha) bilayer states. The phase transition mechanisms were unambiguously determined by comparison of results from fast and slow scans. The Lc(inter)-->L beta(inter) phase transition was shown to involve a continuous change in acyl chain spacing between the rectangular subgel acyl chain unit cell into an hexagonal gel acyl chain unit cell. The mechanism is similar to that for subgel to gel state transitions involving non-interdigitated DPPC bilayers.