The elusive adipose connection

Adipocytes are larger in lymphedematous extremities than in controls

Lymphedema is caused by dysfunctional lymph vessels or as a complication of cancer treatment leading to edema and adipose tissue deposition. One hypothesis is that adipocyte hypertrophy contributes to the volume increase in lymphedema. The aim of the study was to compare adipocyte size in arm and leg lymphedema and controls. The adipocyte size difference was also compared between the arms and legs. Furthermore, any link between adipocyte size difference and gender, lymphedema onset, duration, previous radio- and chemotherapy was studied, as well as any relationship to total excess volume increase in the extremities, body mass index (BMI) and body weight. Adipose tissue biopsies from the lymphedematous and non-affected extremities were taken from 47 patients. The adipocytes sizes were measured using an Olympus PROVIS microscope, Olympus DP50 camera (Olympus, Tokyo, Japan) and ImageJ program (NIH, Bethesda, MD). Additional information was obtained from the Lymphedema Center database. The data were assembled in Excel and statistics was calculated in SPSS^® Statistics 23 (IBM^®, Armonk, NY). The adipocyte size (mean ± SEM) in the lymphedematous extremities was significantly larger, 8880 ± 291 μm², compared to the adipocyte size in the non-affected extremities, where it was 7143 ± 280 μm², i.e. 24% larger (p < .001). The adipocyte size increase was larger in arm than in leg lymphedema. No correlation was found between adipocyte size and gender or onset. However, a negative correlation was found between adipocyte size difference and duration. No correlation was found between adipocyte size and previous chemo- or radiotherapy. There was a positive correlation between adipocyte size and BMI. Hypertrophy of adipocytes was seen in the lymphedematous extremities versus control and contributes to the excess volume.

A tissue-engineered model of the intestinal lacteal for evaluating lipid transport by lymphatics

Lacteals are the entry point of all dietary lipids into the circulation, yet little is known about the active regulation of lipid uptake by these lymphatic vessels, and there lacks in vitro models to study the lacteal-enterocyte interface. We describe an in vitro model of the human intestinal microenvironment containing differentiated Caco-2 cells and lymphatic endothelial cells (LECs). We characterize the model for fatty acid, lipoprotein, albumin, and dextran transport, and compare to qualitative uptake of fatty acids into lacteals in vivo. We demonstrate relevant morphological features of both cell types and strongly polarized transport of fatty acid in the intestinal-to-lymphatic direction. We found much higher transport rates of lipid than of dextran or albumin across the lymphatic endothelial monolayer, suggesting most lipid transport is active and intracellular. This was confirmed with confocal imaging of Bodipy, a fluorescent fatty acid, along with transmission electron microscopy. Since our model recapitulates crucial aspects of the in vivo lymphatic-enterocyte interface, it is useful for studying the biology of lipid transport by lymphatics and as a tool for screening drugs and nanoparticles that target intestinal lymphatics.

Adipose tissue dominates chronic arm lymphedema following breast cancer: an analysis using volume rendered CT images

BACKGROUND

Arm lymphedema is a common complication after breast cancer treatment. Various types of conservative and surgical treatments have aimed at reducing the arm swelling, but most of these have failed due to chronic edema eventually being transformed from an accumulation of lymph fluid to an increased deposition of subcutaneous fat (i.e., to a nonpitting lymphedema). Liposuction is a safe and reliable method for reducing the excess fat without recurring deposition of it. The objective of the present study was to obtain empirical evidence confirming clinical observations of the presence of excess adipose tissue in patients with chronic nonpitting arm lymphedema following breast cancer.

METHODS

A total of 11 women with nonpitting unilateral postmastectomy arm lymphedema were investigated and were treated as follows: The patient's excess arm volume was measured by plethysmography (PG) and, following treatment by liposuction, was observed until complete reduction of the excess volume was achieved. Volume-rendered CT images (VR-CT) and PG were used to analyze arm volumes and excess volume of the lympedematous arm, the respective volumes being compared by use of regression analysis. Liposuction aspirate was analyzed in terms of the distribution of adipose tissue and free fluid (lymph). The aspirate volume (total and fat fraction) was compared both with the excess arm volume measured by VR-CT and PG, and with the excess fat volume measured by VR-CT. The amount of excess adipose tissue in the lymphedematous arm was estimated using VR-CT.

RESULTS

A complete reduction of the excess arm volumes, as measured with PG, was achieved within 6 months, with a mean reduction of 109%, the treated arm thus becoming somewhat smaller than the normal one. Correlations in terms of correlation coefficient (CC) and the coefficient of regression (CR) were all close to 1: The preoperative PG and the VR-CT analyses of (a) the swollen arms of the patients and (b) the excess volume; the total aspirated volume, and the excess volume of the arm, the aspirate fat volume, and the excess fat volume. The aspirate removed under bloodless conditions, achieved by use of a tourniquet, contained 93% adipose tissue. VR-CT was able to estimate the amount of excess adipose tissue in the lymphedematous arm, showing a mean excess amount of fat of 81%.

CONCLUSION

VR-CT measurements correlate well with PG measurements. Excess adipose tissue dominates nonpitting chronic arm lymphedema. This excess volume cannot be removed by use either of conservative regimens or of microsurgery. Liposuction can completely remove the excess adipose tissue, leading to complete reduction of the lymphedema.

Changes in adipocytes and dendritic cells in lymph node containing adipose depots during and after many weeks of mild inflammation

The time course and cellular basis for inflammation-induced hypertrophy of adipose tissue were investigated over 20 weeks in mature male rats. Mild inflammation was induced by subcutaneous injection of 20 microg lipopolysaccharide into one hind-leg three times/week for 4 or 8 weeks, followed by up to 12 weeks 'rest' without intervention. Mean volume and frequency of apoptosis (TUNEL assay) were measured in adipocytes isolated from sites defined by their anatomical relations to lymph nodes, plus numbers of CCL21-stimulated lymph node-derived and adipose tissue-derived dendritic cells. Experimental inflammation increased dendritic cells and adipocyte apoptosis in the locally stimulated popliteal depot and the lymphoid tissue-associated regions of the contralateral popliteal and mesentery and omentum. Responses declined slowly after inflammation ended, but all measurements from the locally stimulated popliteal depot, and the omentum, were still significantly different from controls after 12 weeks rest. The locally stimulated popliteal adipose tissue enlarged by 5% within 4 weeks and remained larger than the control. We conclude that prolonged inflammation induces permanent enlargement, greater adipocyte turnover and increased dendritic cell surveillance in the adjacent adipose tissue and the omentum. The experiment suggests a mechanism for selective hypertrophy of lymphoid tissue-associated adipose tissue in chronic stress and inflammatory disorders, including impaired lymph drainage, Crohn's disease and HIV-associated lipodystrophy, and a link between evolutionary fitness, sexual selection and aesthetically pleasing body symmetry. It would be useful for further study of molecular mechanisms in inflammation-induced local hypertrophy of adipose tissue and development of specific therapies that avoid interference with whole-body lipid metabolism.

Adipose tissue and the immune system

Adipocytes anatomically associated with lymph nodes (and omental milky spots) have many special properties including fatty acid composition and the control of lipolysis that equip them to interact locally with lymphoid cells. Lymph node lymphocytes and tissue dendritic cells acquire their fatty acids from the contiguous adipocytes. Lymph node-derived dendritic cells suppress lipolysis in perinodal adipocytes but those that permeate the adipose tissue stimulate lipolysis, especially after minor, local immune stimulation. Inflammation alters the composition of fatty acids incorporated into dendritic cells, and that of node-containing adipose tissue, counteracting the effects of dietary lipids. Thus these specialised adipocytes partially emancipate the immune system from fluctuations in the abundance and composition of dietary lipids. Prolonged, low-level immune stimulation induces the local formation of more adipocytes, especially adjacent to the inflamed lymph node. This mechanism may contribute to hypertrophy of the mesentery and omentum in chronic inflammatory diseases such as HIV-infection, and in smokers. Paracrine interactions between adipose and lymphoid tissues are enhanced by diets rich in n-6 fatty acids and attentuated by fish oils. The latter improve immune function and body conformation in animals and people. The partitioning of adipose tissue in many depots, some specialised for local, paracrine interactions with other tissues, is a fundamental feature of mammals.