Biomedical subjects

Mikael Jensen

Publications and source records attributed to Mikael Jensen.

7 recordsLinked to original sources

PubMed2005

The importance of dietary composition for efficacy of iron absorption measured in a whole diet that includes rye bread fortified with ferrous fumerate: a radioisotope study in young women.

Fe absorption is affected by many dietary factors. The objective of the present study was to measure the effects of high v. low content of vitamin C, meat and phytic acid in whole diets with Fe-fortified bread on the efficacy of Fe absorption. Thirty-two healthy women with low Fe stores were randomised to three groups, each of which was given two of six test diets containing either low/high amounts of vitamin C, meat or phytic acid, respectively, in a cross-over design. Each diet was served throughout a 5 d period. Fe-fortified rye bread, extrinsically labelled with (59)Fe, was given with all main meals. Fe absorption was determined from whole-body counter measurements of (59)Fe retention. The fractional non-haem Fe absorption (corrected to a 40 % standard absorption by measurements from the reference dose) was 1.9 % v. 3.4 % (P=0.04) for the low/high vitamin C diets, 3.0 % v. 3.5 % (P=0.58) on the low/high meat diets and 4.9 % v. 3.8 % (P=0.24) on the low/high phytic acid diet, respectively. The total Fe absorbed (geometric mean with standard error) varied from 0.43 (se 0.11) mg from the diet with lowest bioavailability to 1.09 (se 0.18) mg from the diet with highest bioavailability (P<0.001). The present whole-diet study indicates that diet composition is a strong predictor of Fe absorption. In the diet with a low content of enhancers and a high content of inhibitors, vitamin C improved non-haem Fe absorption. The total Fe absorption varied 2.5-fold after small alterations of the content of enhancers and inhibitors in the diet.

Absorption↗

PubMed2004

Calcium from milk or calcium-fortified foods does not inhibit nonheme-iron absorption from a whole diet consumed over a 4-d period.

BACKGROUND: Single-meal studies have indicated that calcium inhibits iron absorption in humans. However, numerous dietary factors influence iron absorption, and the effect of calcium may not be as pronounced when calcium is served as part of a whole diet. OBJECTIVE: We investigated the effect of 3 sources of calcium served with the 3 main meals on nonheme-iron absorption from a 4-d diet. DESIGN: (59)Fe absorption was estimated from whole-body retention measurements in 14 women aged 21-34 y, each of whom consumed four 4-d diets in a randomized crossover design. The diets differed in the source of calcium as follows: a basic diet (BD) with a low content of calcium (224 mg Ca/d), a BD with a glass of milk served at each meal (826 mg Ca/d), a BD with calcium lactate (802 mg Ca/d), and a BD with a milk mineral isolate containing calcium (801 mg Ca/d). The 2 latter calcium sources were added to selected foods of the BD (rye bread, white bread, chocolate cake, and orange juice), and these foods were consumed with the 3 meals. All diets provided 13.2 mg Fe/d. RESULTS: No significant differences in nonheme-iron absorption were found between the BD and the BD supplemented with milk, calcium lactate, or the milk mineral isolate [7.4% (95% CI: 5.3%, 10.5%), 5.2% (3.5%, 7.9%), 6.7% (5.0%, 8.9%), and 5.1% (3.2%, 7.9%), respectively; P = 0.34]. CONCLUSION: Consumption of a glass of milk with the 3 main meals or of an equivalent amount of calcium from fortified foods does not decrease nonheme-iron absorption from a 4-d diet.

Adult↗

PubMed2003

The inhibitor thiomandelic acid binds to both metal ions in metallo-beta-lactamase and induces positive cooperativity in metal binding.

Thiomandelic acid is a simple, broad spectrum, and reasonably potent inhibitor of metallo-beta-lactamases, enzymes that mediate resistance to beta-lactam antibiotics. We report studies by NMR and perturbed angular correlation (PAC) spectroscopy of the mode of binding of the R and S enantiomers of thiomandelic acid, focusing on their interaction with the two metal ions in cadmium-substituted Bacillus cereus metallo-beta-lactamase. The 113Cd resonances are specifically assigned to the metals in the two individual sites on the protein by using 113Cd-edited 1H NMR spectra. Each enantiomer of thiomandelate produces large downfield shifts of both 113Cd resonances and changes in the PAC spectra, which indicate that they bind such that the thiol of the inhibitor bridges between the two metals. For R-thiomandelate, this is unambiguously confirmed by the observation of scalar coupling between Halpha of the inhibitor and both cadmium ions. The NMR and PAC spectra reveal that the two chiral forms of the inhibitor differ in the details of their coordination geometry. The complex with R-thiomandelate, but not that with the S-enantiomer, shows evidence in the PAC spectra of a dynamic process in the nanosecond time regime, the possible nature of which is discussed. The thiomandelate complex of the mononuclear enzyme can be detected only at low metal to enzyme stoichiometry; the relative populations of mononuclear and binuclear enzyme as a function of cadmium concentration provide clear evidence for positive cooperativity in metal ion binding in the presence of the inhibitor, in contrast to the negative cooperativity observed in the free enzyme.

Bacillus cereus↗

PubMed2003

Nonheme-iron absorption from a phytate-rich meal is increased by the addition of small amounts of pork meat.

BACKGROUND: Muscle tissue from various sources is known to promote nonheme-iron absorption. However, systematic studies of the dose dependency of this effect of meat on iron absorption from an inhibitory meal with low amounts of meat are lacking. OBJECTIVE: We investigated the dose-response effect of small amounts of meat on nonheme-iron absorption from a meal presumed to have low iron bioavailability. DESIGN: Forty-five healthy women with a mean (+/-SD) age of 24 +/- 3 y were randomly assigned to 1 of 3 groups, each of which was served (A) a basic meal (rice, tomato sauce, pea purée, and a wheat roll) and (B) the basic meal with either 25, 50, or 75 g pork (longissimus muscle). Meal A contained 2.3 mg nonheme iron, 7.4 mg vitamin C, and 220 mg (358 micro mol) phytate. Each meal was served twice, and the order of the meals was ABBA or BAAB. The meals were extrinsically labeled with (55)Fe or (59)Fe. Iron absorption was determined from measurements of (59)Fe whole-body retention and the activity of (55)Fe and (59)Fe in blood samples. RESULTS: Twenty-five grams meat did not increase nonheme-iron absorption significantly (P = 0.13), whereas absorption increased 44% (P < 0.001) and 57% (P < 0.001), respectively, when 50 and 75 g meat were added to the basic meal. In absolute values, this corresponds to an absorption that was 2.6% and 3.4% higher, respectively, than that with the basic meal after adjustment of the data to a level of 40% absorption from a reference dose. CONCLUSION: Small amounts of meat (>or=50 g) significantly increase nonheme-iron absorption from a phytate-rich meal low in vitamin C.

Adult↗

PubMed2003

A novel dual radio- and stable-isotope method for measuring calcium absorption in humans: comparison with the whole-body radioisotope retention method.

BACKGROUND: Dietary calcium absorption can be determined only with the use of isotope techniques. Currently used isotope techniques require exclusive equipment or are not true tracer approaches. OBJECTIVE: The objective was to compare a dual-isotope method combining radioisotopes and stable isotopes with a whole-body radioisotope retention method for measuring calcium absorption. DESIGN: Seven healthy adults aged 21-27 y consumed a test meal containing 63 +/- 14 (macro x +/- SD) mg Ca together with a water solution of (47)Ca (0.11 MBq). One hour after ingestion, 18 mg (44)Ca was administered intravenously. All feces and urine were collected for 5 and 6 d, respectively. Calcium absorption was estimated from whole-body retention of the radioisotope 12 times over 3 wk after ingestion and from the excretion of (47)Ca and (44)Ca in a 24-h urine sample collected on day 2. (44)Ca in urine was determined by inductively coupled plasma mass spectrometry. RESULTS: Mean (+/- SD) calcium absorption was 75 +/- 9% with the dual-isotope method and was 74 +/- 8% with the whole-body radioisotope retention method. There was a high degree of agreement between the methods. CONCLUSION: The dual-isotope method is a valid approach for measuring calcium absorption from a single meal.

Administration, Oral↗

PubMed2003

Increasing the cooking temperature of meat does not affect nonheme iron absorption from a phytate-rich meal in women.

The effect of increasing cooking temperatures of meat on nonheme iron absorption from a composite meal was investigated. Cysteine-containing peptides may have a role in the iron absorption enhancing effect of muscle proteins. Heat treatment can change the content of sulfhydryl groups produced from cysteine and thereby affect iron absorption. Twenty-one women (25 +/- 3 y) were served a basic meal without meat and two other meals consisting of the basic meal plus 75 g of pork meat cooked at 70, 95 or 120 degrees C. The meals were extrinsically labeled with (55)Fe or (59)Fe. Iron absorption was determined from measurements of whole-body (59)Fe retention and the activity of (55)Fe and (59)Fe in blood samples. Nonheme iron absorptions were 0.9 (0.5-4.0)% (P = 0.06), 0.7 (0.4-3.9)% (P = 0.1) and 2.0 (1.3-3.1)% (P < 0.001) greater when meat cooked at 70, 95 or 120 degrees C, respectively, was added to the basic meal. Increasing the cooking temperature of meat did not impair nonheme iron absorption compared with cooking at 70 degrees C. Because the cysteine content of meat decreased with increasing cooking temperature, this argues against a specific contribution of sulfhydryl groups from cysteine residues in the promotion of nonheme iron absorption by meat proteins.

Adult↗

PubMed2002

[The working brain--how does it look like?].

Numerous brain functions, such as awareness of surroundings, control of movements, thoughts, and memory have always been a kind of mystery, which has provoked human curiosity and thus inspired research in many areas. The present paper gives an overview on imaging research of the human brain's functions. The historical progress is briefly reviewed with the emphasis on major Danish contributions. The major methods of mapping brain functions and their biological basis are mentioned. These methods are positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). They are highly technological and generate enormous amounts of data. Thus, data analysis will per se be a research area in brain imaging. Finally, several examples of the authors' results on functional activation are dealt with. These examples aim to illustrate the research area and its contribution to our increased knowledge of the working brain.

Acoustic Stimulation↗