Identification of a novel tetrameric structure for human apolipoprotein-D.

Apolipoprotein-D is a 25 kDa glycosylated member of the lipocalin family that folds into an eight-stranded ß-barrel with a single adjacent α-helix. Apolipoprotein-D specifically binds a range of small hydrophobic ligands such as progesterone and arachidonic acid and has an antioxidant function that is in part due to the reduction of peroxidised lipids by methionine-93. Therefore, apolipoprotein-D plays multiple roles throughout the body and is protective in Alzheimer's disease, where apolipoprotein-D overexpression reduces the amyloid-ß burden in Alzheimer's disease mouse models. Oligomerisation is a common feature of lipocalins that can influence ligand binding. The native structure of apolipoprotein-D, however, has not been conclusively defined. Apolipoprotein-D is generally described as a monomeric protein, although it dimerises when reducing peroxidised lipids. Here, we investigated the native structure of apolipoprotein-D derived from plasma, breast cyst fluid (BCF) and cerebrospinal fluid. In plasma and cerebrospinal fluid, apolipoprotein-D was present in high-molecular weight complexes, potentially in association with lipoproteins. In contrast, apolipoprotein-D in BCF formed distinct oligomeric species. We assessed apolipoprotein-D oligomerisation using native apolipoprotein-D purified from BCF and a suite of complementary methods, including multi-angle laser light scattering, analytical ultracentrifugation and small-angle X-ray scattering. Our analyses showed that apolipoprotein-D predominantly forms a ∼95 to ∼100 kDa tetramer. Small-angle X-ray scattering analysis confirmed these findings and provided a structural model for apolipoprotein-D tetramer. These data indicate apolipoprotein-D rarely exists as a free monomer under physiological conditions and provide insights into novel native structures of apolipoprotein-D and into oligomerisation behaviour in the lipocalin family.

Concentration of aluminium in breast cyst fluids collected from women affected by gross cystic breast disease.

Gross cystic breast disease (GCBD) is the most common benign breast disorder, but the molecular basis of cyst formation remains to be identified. If the use of aluminium-based antiperspirant salts is involved in the etiology of gross breast cyst formation, it might be expected that aluminium would be at elevated levels in human breast cyst fluid (BCF). Aluminium was measured by ICP-MS in 48 samples of BCF, 30 samples of human blood serum and 45 samples of human breast milk at different stages of lactation (colostrum, intermediate, mature). The median level of aluminium in apocrine type I BCF (n = 27, 150 microg l(-1)) was significantly higher than in transudative type II BCF (n = 21, 32 microg l(-1); P < 0.0001). By comparison, aluminium measurements gave a median concentration of 6 microg l(-1) in human serum and 25 microg l(-1) in human breast milk, with no difference between colostrum, intermediate and mature milk. Levels of aluminium were significantly higher in both types of BCF than in human serum (P < 0.0001). However when compared with human breast milk, aluminium levels were only significantly higher in apocrine type I BCF (P < 0.0001) and not in transudative type II BCF (P = 0.152). It remains to be identified why such high levels of aluminium were found in the apocrine type I BCF and from where the aluminium originated. However, if aluminium-based antiperspirants are found to be the source and to play any causal role in development of breast cysts, then it might become possible to prevent this common breast disorder.

Cytokines in human breast cyst fluid.

Gross cystic breast disease is a common benign disorder in which palpable cysts occur in the breast and are normally treated by aspiration of the contents. The cysts are classified as either Type 1, containing a high level of potassium ions and a low level of sodium ions, or as Type 2, with low potassium and high sodium ion concentrations. Steroid sulphatase activity in MDA-MB-231 and MCF-7 cell lines is regulated by exogenous breast cyst fluid (BCF), possibly because of cytokines in the BCF. A screening method was used to determine the range of cytokines in eight BCFs, four of each type. This was an array system, which uses antibodies immobilised on a membrane to qualitatively detect 79 different cytokines or growth factors. Nine cytokines were detected well above background levels: all were found in both types of BCF, but only epidermal growth factor (EGF) was higher in Type 1. All the other factors were higher in Type 2 BCF. Two of these cytokines, IL-6 and EGF, have previously been suggested to affect steroid sulphatase expression and several (MIP-1beta, IL-8, NAP-2) are known to affect MCF-7 cell chemotaxis. In addition two cytokines were measured by ELISA in 57 BCFs, and both IL-1beta and IL-13 were found in BCF, with significantly higher amounts of IL-1beta in Type 1 than Type 2 BCF (35.5+/-4.4 pg/ml versus 9.9+/-2.9 pg/ml).

Cytological and biochemical studies of breast cyst fluid.

We determined the biochemical composition of fluid aspirated from 52 breast cysts and classified the cysts into types I and II on the basis of the potassium-to-sodium (K/Na) ratio in the fluid. In this study, we confirmed the presence of prostate-specific antigen (PSA) in some breast cyst fluids, regardless of whether cysts were type 1 or type 2, or benign or malignant. On immunohistochemical study, we found no direct correlation between the presence of PSA and progesterone receptors, which is at odds with the results of earlier reports. Current practice in cytologic study appears to favor the examination of bloody fluid. In this study, two samples found to contain malignant cells were cloudy or turbid. We therefore recommend that all cloudy or turbid cyst fluids should be subjected to cytologic examination. This study indicated that the potassium and sodium concentrations were not the same in multiple cysts in the same individuals. In addition, apocrine cells were observed in both type 1 and type 2 cysts. Therefore, breast cyst type cannot predict the natural history of cystic changes or indicate the likelihood of cancer. The finding of malignancy in two patients with type 2 cysts also supports this argument.

Conjugated bile acids in breast cyst fluids: relationship to cation-related cyst subpopulations.

Gross cystic breast disease is a benign lesion occurring in 7% of adult women. Apocrine changes of epithelium lining the breast cysts cause a higher risk of developing breast cancer. According to the possible role of bile acids in the pathogenesis of cancer, we analysed breast cyst fluids aspirated from 96 women for distribution of conjugated bile acid concentrations in the two subsets of breast cysts. Bile acid levels were correlated to K+ concentrations (P < 0.0001) and mean value was higher in Na/K < 3 metabolically active apocrine cyst as compared with Na/K > 3 flattened cyst (P < 0.001). Because bile acids could play an important role in the pathogenesis and growth of breast cancer, the significantly higher intracystic concentrations of these carcinogen compounds in apocrine Type I cysts might provide a further biological explanation as to why women with apocrine changes may be at higher breast cancer risk and could be useful for the biochemical knowledge occurring in the different functional stages of the gross breast cysts.