Biology subjects

Hammer, N.

Publications and source records attributed to Hammer, N..

3 recordsLinked to original sources

bioRxiv2024

Impact of high fat diet and exercise on bone and bile acid metabolism in rats

BackgroundBile acids help facilitate the intestinal lipids absorption, and have endocrine activity in glucose, lipid and bone metabolism. Obesity and exercise influence bile acid metabolism and have opposite effects in bone. This given study investigates if regular exercise helps mitigate the adverse effects of obesity on bone, potentially by reversing alterations in bile acid metabolism. MethodsFour-month-old female Sprague Dawley rats either received high fat diet (HFD) or chow-based standard diet (lean controls). During the 10-month study period, half of the animals performed 30 min of running at moderate speed on five consecutive days followed by two days of rest. The other half was kept inactive (inactive controls). At study end, bone quality was assessed by micro computed tomography and biomechanical testing. Bile acids were measured in serum and stool. ResultsHFD feeding was related to reduced trabecular (-33%, p=1.14x10-7) and cortical (-21%, p=2.9x10-8) bone mass, and lowered femoral stiffness (12-41%, p=0.005). Furthermore, HFD decreased total bile acids in serum (-37%, p=1.0x10-6), but increased bile acids in stool (+2-fold, p=7.3x10-9). These quantitative effects were accompanied by changes in the relative abundance of individual bile acids. The concentration of serum bile acids correlated positively with all cortical bone parameters (r=0.593 - 0.708), whilst stool levels showed inverse correlations at cortical (r=-0.651 - -0.805) and trabecular level (r=-0.656 - -0.750). Exercise improved some trabecular and cortical bone quality parameters (+11-31%, p=0.043 to 0.001) in lean controls, but failed to revert the bone loss related to HFD. Similarly, changes in bile acid metabolism were not mitigated by exercise. ConclusionProlonged HFD consumption induced quantitative and qualitative alterations in bile acid metabolism, accompanied by bone loss. Tight correlations between bile acids and structural indices of bone quality support further functional analyses on the potential role of bile acids in bone metabolism. Regular moderate exercise improved trabecular and cortical bone quality in lean controls but failed mitigating the effects related to HFD in bone and bile acid metabolism.

molecular biology↗

bioRxiv2021

Mechanical Metric for Skeletal Biomechanics Derived from Spectral Analysis of Stiffness matrix

A new metric for the quantitative and qualitative evaluation of bone stiffness is introduced. It is based on the spectral decomposition of stiffness matrix computed with finite element method. The here proposed metric is defined as an amplitude rescaled eigenvalues of stiffness matrix. The metric contains unique information on the principal stiffness of bone and reflects both bone shape and material properties. The metric was compared with anthropometrical measures and was tested for sex sensitivity on pelvis bone. Further, the smallest stiffness of pelvis was computed under a certain loading condition and analyzed with respect to sex and direction. The metric complements anthropometrical measures and provides a unique information about the smallest bone stiffness independent from the loading configuration and can be easily computed by state-of-the-art subject specified finite element algorithms.

bioinformatics↗

bioRxiv2021

Bone Mineral Density modelled as a Random Field: a Feasibility Study on Pelvic Bone

Background and ObjectiveCapturing the population variability of bone properties is of paramount importance to biomedical engineering. The aim of the present paper is to describe variability and correlations in bone mineral density with a spatial random field inferred from routine computed tomography data. MethodsRandom fields were simulated by transforming pairwise uncorrelated Gaussian random variables into correlated variables through the spectral decomposition of an age-detrended correlation matrix. The validity of the random field model was demonstrated in the spatiotemporal analysis of bone mineral density. The similarity between the computed tomography samples and those generated via random fields was analyzed with the energy distance metric. ResultsThe random field of bone mineral density was found to be approximately Gaussian/slightly left-skewed/strongly right-skewed at various locations. However, average bone density could be simulated well with the proposed Gaussian random field for which the energy distance, i.e., a measure that quantifies discrepancies between two distribution functions, is convergent with respect to the number of correlation eigenpairs. ConclusionsThe proposed random field model allows the enhancement of computational biomechanical models with variability in bone mineral density, which could increase the usability of the model and provides a step forward in in-silico medicine.

biophysics↗