Gert Meijer

Tissue engineering of bone

Bone is a dynamic, highly vascularized tissue with the unique capacity to heal and to remodel depending on line of stress (Buckwalter et al, 1995ab). It exhibits the unlikely combination of high compressive strength and tensile strength due to the composite of calcium phosphate salts (hydroxyapatite) and collagen, respectively (Yaszemski et al, 1996a). It is difficult to find materials to mimic such a complex system when filling bone defects. However, current research capitalizes on the dynamic properties of bone by providing a biodegradable scaffold to guide healing.

Effects of green tea, black tea and dietary lipophilic antioxidants on LDL oxidizability and atherosclerosis in hypercholesterolaemic rabbits

The hypothesis that tea or dietary lipid-soluble antioxidants reduce atherogenesis by lowering the oxidizability of low-density lipoprotein (LDL) was investigated. Five groups of 20 female New Zealand white rabbits were fed a restricted amount of a high-fat (30 en%) semipurified diet supplemented with cholesterol (0.15%, w/w) for 21 weeks. The vitamin E content of the control diet was 40 mg/kg diet. The animals received either green tea or black tea in their drinking water or vitamin E (200 mg/kg diet) or beta-carotene (20 mg/kg). The serum cholesterol concentrations (in the order of 18-23 mmol/l) were not significantly different between the groups. Vitamin E was substantially increased as compared to controls in vitamin E supplemented animals (3-fold within 8 weeks in plasma and LDL; P < 0.01) and weakly (1.2-fold) by green and black tea (P < 0.05). Green tea consumption tended to reduce aortic lesion formation by 31% (24 +/- 3.2% versus 35 +/- 5.7% for control animals P = 0.11), while black tea, vitamin E and beta-carotene had no effect. This was in contrast to the resistance of isolated LDL to oxidation induced at high copper concentration. Green and black tea induced a 13% and 15% (P < 0.05) prolongation of the lag phase, respectively, with a correspondingly lower oxidation rate, while vitamin E increased the lag phase by 63% (P < 0.01) with a concomitant diminution of the oxidation rate and beta-carotene had no effect. Regression analysis showed that there was no relationship between the extent of atherosclerosis and LDL oxidizability or plasma malondialdehyde as marker of in vivo lipid peroxidation. The results of the present study raise the question whether LDL oxidizability (at least when tested at high induction rate ex vivo) is a primary causal mechanism in atherosclerosis in the cholesterol-fed rabbit. The suitability of the cholesterol-fed rabbit with extreme hypercholesterolaemia as a model to study antiatherosclerotic properties of dietary antioxidants, such as the tested polyphenols, is discussed.

Spreads enriched with plant sterols, either esterified 4,4-dimethylsterols or free 4-desmethylsterols, and plasma total- and LDL-cholesterol concentrations.

In a 9-week study seventy-six healthy adult volunteers with an average age of 44 (SD 11) years, with baseline plasma total cholesterol levels below 8 mmol/l, received in a balanced, double-blind, crossover design, a total of three different table spreads for personal use. Two spreads were fortified either with free (non-esterified) vegetable-oil sterols, mainly from soyabean oil (31 g sterol equivalents/kg; 0.8 g/d) or sheanut-oil sterols (133 g sterol equivalents/kg; 3.3 g/d). One spread was not fortified (control). Average intake of spread was 25 g/d for 3 weeks. None of the spreads induced changes in blood clinical chemistry or haematology. Plasma total- and LDL-cholesterol concentrations were statistically significantly reduced by 3.8% and 6% (both 0.19 mmol/l) respectively, for the spread enriched with free soyabean-oil sterols compared with the control spread. The spread enriched with sheanut-oil sterols did not lower plasma total- and LDL-cholesterol levels. None of the plant-sterol-enriched spreads affected plasma HDL-cholesterol concentrations. Plasma-lipid-standardized concentrations of alpha- plus beta-carotene were not statistically significantly affected by the soyabean-oil sterol spread in contrast to lipid-standardized plasma lycopene levels which showed a statistically significant decrease (9.5%). These findings indicate that a daily intake of free soyabean-oil sterols as low as 0.8 g added to a spread is effective in lowering blood total- and LDL-cholesterol levels with limited effects on blood carotenoid levels. The lowering in total- and LDL-cholesterol blood levels due to consumption of the vegetable-oil-sterol-enriched spread may be helpful in reducing the risk of CHD for the population.

Effect of dietary elaidic versus vaccenic acid on blood and liver lipids in the hamster

Male hamsters (30 per group) were fed five different semi-purified diets ad libitum. The diets, containing 30% of energy (en%) as fat, differed in their dietary fat composition (specified fatty acids exchanged at 10 en%) and were fed for 4 weeks. The five fatty acids compared in mixed triglycerides were elaidic acid (C18:1 9t), vaccenic acid (C18:1 11t), their cis-counterpart oleic acid (C18:1 9c), medium-chain fatty acids (MCFA; C8:0 and C10:0), and palmitic acid (C16:0). Compared with oleic acid, dietary MCFA and palmitic acid tended to increase blood cholesterol levels in the hamsters. The effect of elaidic and vaccenic acid on blood cholesterol did not differ from that of oleic acid. When elaidic acid and vaccenic acids were compared directly, the ratio of LDL/HDL-cholesterol in plasma was significantly higher in hamsters fed vaccenic acid than in those fed elaidic acid, and elaidic acid was incorporated at low levels, but more efficiently than vaccenic acid at the sn-2 position of platelet phospholipids. Biological consequences of this low incorporation are considered unlikely as levels of arachidonic acid (C20:4 n-6) and docosohexaenoic acid (C22:6 n-3) in the platelet phospholipids of all dietary groups did not differ. With respect to the effect on the LDL/HDL-cholesterol ratio, elaidic acid may be preferable to vaccenic acid. We conclude that this animal study does not provide evidence for the suggestion, based on epidemiological observations, that elaidic acid would be more detrimental to cardiovascular risk than vaccenic acid.

Clinical application of human mesenchymal stromal cells for bone tissue engineering.

The gold standard in the repair of bony defects is autologous bone grafting, even though it has drawbacks in terms of availability and morbidity at the harvesting site. Bone-tissue engineering, in which osteogenic cells and scaffolds are combined, is considered as a potential bone graft substitute strategy. Proof-of-principle for bone tissue engineering using mesenchymal stromal cells (MSCs) has been demonstrated in various animal models. In addition, 7 human clinical studies have so far been conducted. Because the experimental design and evaluation parameters of the studies are rather heterogeneous, it is difficult to draw conclusive evidence on the performance of one approach over the other. However, it seems that bone apposition by the grafted MSCs in these studies is observed but not sufficient to bridge large bone defects. In this paper, we discuss the published human clinical studies performed so far for bone-tissue regeneration, using culture-expanded, nongenetically modified MSCs from various sources and extract from it points of consideration for future clinical studies.

Sterol balance and cholesterol absorption in inbred strains of rabbits hypo- or hyperresponsive to dietary cholesterol

In 2 inbred strains of rabbits with high or low response of plasma cholesterol to dietary cholesterol, excretion of steroids in the feces and efficiency of cholesterol absorption were determined. Rates of whole-body cholesterol synthesis, measured as fecal excretion of bile acids and neutral steroids minus cholesterol intake, were similar in hypo- and hyperresponders fed a low-cholesterol (8 mumol/100 g) diet. Transfer of the rabbits to a high-cholesterol (182 mumol/100 g) diet caused an increase in fecal bile acid excretion in hypo- but not in hyperresponders. Dietary cholesterol did not affect neutral steroid excretion in either rabbit strain. Hyperresponders tended to accumulate more cholesterol in their body than did hyporesponders. After the rabbits were switched back from the high- to the low-cholesterol diet, rates of whole-body cholesterol synthesis were significantly higher in the hypo- than in the hyperresponders. With the use of the simultaneous oral administration of [3H]cholesterol and beta-[14C]sitosterol, hyperresponders were found to absorb significantly higher percentages of cholesterol than hyporesponders. It is concluded that the differences in stimulation of bile acid excretion after cholesterol feeding and the efficiency of cholesterol absorption are important determinants of the phenomenon of hypo- and hyperresponsiveness in the 2 inbred rabbit strains.

The influence of transportation stress on selected nutritional parameters to establish the necessary minimum period for adaptation in rat feeding studies

The optimal length of the adaptation period after transportation of rats, to be used in nutritional studies, was investigated in this study. After intracontinental transportation of rats by car and by air to and from the laboratory for a total period of 15 h, measurements were carried out for a period of 3 weeks after transport. Control and transported animals were housed in the same laboratory before and after transportation. During transport the animals had access to food and water. As blood collection could also cause stress, a factorial design was carried out with transport and blood collection as main factors. Transport or blood collection did not cause significant effects on the following parameters: body weight, growth, clinical observation, and blood enzyme activities of LDH and ASAT. Water intake was significantly increased after transport. Food intake did not show consistent effects after transport or blood collection. Unexpectedly, blood corticosterone levels were significantly lower in the transported animals at day 1 after transport. After 3 days these levels were back to normal. Blood glucose, blood free fatty acids and blood urea nitrogen concentrations were incidentally decreased, whereas total cholesterol levels showed an incidental rise in the transported rats. The open-field behaviour test revealed no clear-cut results concerning the effects of transport or blood collection on faeces production, rearing and ambulation. Our results indicate that after intracontinental transport, an adaptation period of 3 days appears to be sufficient for rats to be used in nutritional studies.

Dose painting by contours versus dose painting by numbers for stage II/III lung cancer: Practical implications of using a broad or sharp brush

PURPOSE Local recurrence rates are high in patients with locally advanced NSCLC treated with 60 to 66 Gy in 2 Gy fractions. It is hypothesised that boosting volumes with high SUV on the pre-treatment FDG-PET scan potentially increases local control while maintaining acceptable toxicity levels. We compared two approaches: threshold-based dose painting by contours (DPBC) with voxel-based dose painting by numbers (DPBN). MATERIALS AND METHODS Two dose painted plans were generated for 10 stage II/III NSCLC patients with 66 Gy at 2-Gy fractions to the entire PTV and a boost dose to the high SUV areas within the primary GTV. DPBC aims for a uniform boost dose at the volume encompassing the SUV 50%-region (GTV(boost)). DPBN aims for a linear relationship between the boost dose to a voxel and the underlying SUV. For both approaches the boost dose was escalated up to 130 Gy (in 33 fractions) or until the dose limiting constraint of an organ at risk was met. RESULTS For three patients (with relatively small peripheral tumours) the dose within the GTV could be boosted to 130 Gy using both strategies. For the remaining patients the boost dose was confined by a critical structure (mediastinal structures in six patients, lungs in one patient). In general the amount of large brush DPBC boosting is limited whenever the GTV(boost) is close to any serial risk organ. In contrast, small brush DPBN inherently boosts at a voxel-by-voxel basis allowing significant higher dose values to high SUV voxels more distant from the organs at risk. We found that the biological SUV gradients are reasonably congruent with the dose gradients that standard linear accelerators can deliver. CONCLUSIONS Both large brush DPBC and sharp brush DPBN techniques can be used to considerably boost the dose to the FDG avid regions. However, significantly higher boost levels can be obtained using sharp brush DPBN although sometimes at the cost of a less increased dose to the low SUV regions.

Imaging of oesophageal cancer with FDG-PET/CT and MRI

Integrated 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG) PET/CT and magnetic resonance imaging (MRI) with functional features of diffusion-weighted imaging (DWI) are advancing imaging technologies that have current and future potential to overcome important limitations of conventional staging methods in the management of patients with oesophageal cancer. PET/CT has emerged as an important part of the standard work-up of patients with oesophageal cancer. Besides its important ability to detect unsuspected metastatic disease, PET/CT may be useful in the assessment of treatment response, radiation treatment planning, and detection of recurrent disease. In addition, high-resolution T2-weighted MRI and DWI have potential complementary roles. Recent improvements in MRI protocols and techniques have resulted in better imaging quality with the potential to bring improvement in staging, radiation treatment planning, and the assessment of treatment response. Optimal use and understanding of PET/CT and MRI in oesophageal cancer will contribute to the impact of these advancing technologies in tailoring treatment to the individual patient and achieving best possible outcomes. In this article, we graphically outline the current and potential future roles of PET/CT and MRI in the multidisciplinary management of oesophageal cancer.

Effect of structure and form on the ability of plant sterols to inhibit cholesterol absorption in hamsters.

We investigated the effect of three types of plant sterols (4-desmethylsterols, 4,4′-dimethylsterols, and pentacyclic triterpene alcohols) in three forms (free, esterified with FA, or with phenolic acids) on cholesterol absorption. Plant sterol fractions derived from soybean (99% 4-desmethylsterols), rice bran (70% 4,4′-dimethylsterols), or shea nut (89% pentacyclic triterpene alcohols) were fed to male hamsters (n=20/group) as free sterols or esterified with FA or phenolic acids (cinnamic or ferulic). Cholesterol absorption was measured after 5–8.5 (mean, 7) wk by a dual-isotope technique. Soybean sterol intake significantly reduced cholesterol absorption efficiency (23%) and plasma total cholesterol (11%). Rice bran sterols tended to lower cholesterol absorption efficiency by 7% and plasma total cholesterol by 5%, whereas shea nut sterols had no effect. In hamsters, dietary 4-desmethylsterols were more effective than 4,4′-dimethylsterols in lowering cholesterol absorption and levels of cholesterol in blood. Pentacyclic triterpene alcohols had no effect on the absorption of cholesterol or on its level in blood. Esterification with FA did not impair the ability of 4-desmethylsterols and 4,4′-dimethylsterols to inhibit cholesterol absorption, whereas esterification with phenolic acids reduced this ability. This study supports the use of 4-desmethylsterols, esterified with FA to increase solubility, as the most effective cholesterol-lowering plant sterols in the diet.