Milk fat globules: Fatty acid composition, size and in vivo regulation of fat liquidity

Timmen, H.; Patton, Stuart

doi:10.1007/bf02535669

Cited by 154 publications

(122 citation statements)

References 22 publications

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“…The incorporation of unsaturated fatty acids into otherwise palmitic-acid-rich TGs (Fig. 3b,c) would lower the molecular melting temperature and introduce more fluidity to the TG structure [40]. It is evident from the data that a proportion of tripalmitin of 20% or less does not induce beta cell cytotoxicity, whereas if tripalmitin forms greater than 60% of the TG, more than 20% cell death occurs (Figs.…”

Section: Discussionmentioning

confidence: 94%

Adverse physicochemical properties of tripalmitin in beta cells lead to morphological changes and lipotoxicity in vitro

et al. 2005

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Aims/hypothesis: Long-term exposure of beta cells to lipids, particularly saturated fatty acids in vitro, results in cellular dysfunction and apoptosis (lipotoxicity); this could contribute to obesity-related diabetes. Our aims were to relate cell death to intracellular triglyceride concentration, composition and localisation following incubation of INS1 cells in saturated and unsaturated NEFA in high and low glucose concentrations. Materials and methods: In sulin-producing INS1 cells were cultured (24 h; 3 and 20 mmol/l glucose) with palmitic, oleic or linoleic acids and the resulting intracellular lipids were analysed by gas chromatography and microscopy. Cell death was determined by quantitative microscopy and 3-(4,5-dimethlthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and glucose-stimulated insulin secretion by ELISA. Results: All NEFA (0.5 mmol/l, 0.5% albumin) inhibited glucose-stimulated (20 mmol/l) insulin secretion. Cytotoxicity was evident only with palmitic acid (p<0.05), in which case intracellular triglyceride consisted largely of tripalmitin in angular-shaped dilated endoplasmic reticulum. Cytotoxicity and morphological disruption were reduced by addition of unsaturated NEFA. Triglyceridecontent (control cells; 14.5 ng/μg protein) increased up to 10-fold following incubation in NEFA (oleic acid 153.2 ng/μg protein; p<0.05) and triglyceride and phospholipid fractions were both enriched with the specific fatty acid added to the medium (p<0.05). Conclusions/ interpretation: In INS1 cells, palmitic acid is converted in the endoplasmic reticulum to solid tripalmitin (melting point >65C), which could induce endoplasmic reticulum stress proteins and signal apoptosis; lipid-induced apoptosis would therefore be a consequence of the physicochemical properties of these triglycerides. Since cellular triglycerides composed of single species of fatty acid are not likely to occur in vivo, destruction of beta cells by saturated fatty acids could be predominantly an in vitro scenario.

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Section: Discussionmentioning

confidence: 94%

Adverse physicochemical properties of tripalmitin in beta cells lead to morphological changes and lipotoxicity in vitro

et al. 2005

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“…Pauloin et al (2010) have shown in mouse mammary epithelial cells that UFA modify CLD proliferation and size and protein synthesis. Timmen and Patton (1988) have suggested that the CLD rich in UFA might reach the apical pole of the lactocyte faster than the CLD poor in UFA. In this case, the CLD growth during cell migration would be limited and result in the secretion of smaller MFG.…”

Section: Discussionmentioning

confidence: 99%

Relationships between milks differentiated on native milk fat globule characteristics and fat, protein and calcium compositions

Couvreur

Hurtaud

2017

Animal

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Many studies have shown that milk fat globule (MFG) diameter varies in dairy cows in relation to diet and/or breed. However, the mechanisms governing the size of the fat globules remain hypothetical. Our objective was to determine the variable biochemical characteristics (fat, protein, fatty acids (FA), casein and calcium (Ca) contents) between individual milk which differed in both MFG diameter and membrane content, in order to speculate about the links between milk synthesis and MFG secretion. With this aim, we built five databases of individual milk samples from 21 experiments performed between 2003 and 2011. Three of them grouped data from trials dealing with breed/diet effects and included information about: (i) MFG size/membrane, fat and protein contents (n = 982), (ii) previous parameters plus FA profile (n = 529) and (iii) previous parameters plus true protein composition and calcium contents (n = 101). A hierarchical clustering analysis performed on these three databases yielded four groups differing in the MFG characteristics. We observed significant differences among groups for the following parameters: (i) fat content and fat : protein ratio; (ii) de novo and polyunsaturated FA contents; (iii) Ca contents. These relationships could result from potential process regulating the synthesis and secretion of MFG: (i) the apical membrane turnover for MFG secretion and (ii) cytoplasmic lipid droplet formation in the lactocyte during its migration from the basal to the apical pole. The two other databases grouped data from trials dealing with milking frequency (n = 211), milking kinetics and milk type (residual v. cisternal) (n = 224). They were used to study the relationships between the size of the MFG and milk composition for high native fat contents (from 60 up to 100 g/kg in residual milks). We observed curvilinear relationships between the size of the MFG and fat content, as well as with the fat : protein ratio. This result suggests that MFG diameter reaches a threshold but mechanisms are still unknown.

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“…The SCD catalyzed reaction involves cytochrome b 5 , NAD(P)-cytochrome b 5 reductase and molecular oxygen and the CoA ester of fatty acids as a substrate (Palmquist et al, 2005). Activity of SCD in the ruminant mammary gland is thought to occur as a mechanism to maintain and regulate the fluidity of milk to ensure efficient ejection from the mammary glands (Timmen and Patton, 1988). Stearoyl and palmitoyl-CoA are the preferred substrates for SCD with 18:0 to OA being the predominant precursor:product of SCD in the bovine mammary epithelial cell (bMEC) (Palmquist et al, 2005;Bernard et al, 2008).…”

Section: Mammary Lipogenesismentioning

confidence: 99%

“…It is well established that endogenous synthesis of OA via the action of SCD on 18:0 in the mammary gland is an important point of regulation in milk TAG synthesis and maintenance of milk fat fluidity. In addition to fatty acid chain length, degree of unsaturation and the presence of a cis or trans double bond, the maintenance of milk fat globule fluidity also requires that most fatty acids are esterified at specific positions in milk fat TAG to ensure that milk fat has a melting point at or below 398C (Timmen and Patton, 1988). Under certain conditions, decreases in the availability of 18:0 for endogenous OA synthesis combined with an increase in trans 18:1 at the mammary gland have been proposed as a possible mechanism to explain part of the decrease in milk fat secretion during diet-induced MFD (Loor and Herbein, 2003;.…”

mentioning

confidence: 99%

Role of trans fatty acids in the nutritional regulation of mammary lipogenesis in ruminants

Shingfield

Bernard

Leroux

et al. 2010

Animal

333

427

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Fat is an important constituent contributing to the organoleptic, processing and physical properties of ruminant milk. Understanding the regulation of milk fat synthesis is central to the development of nutritional strategies to enhance the nutritional value of milk, decrease milk energy secretion and improve the energy balance of lactating ruminants. Nutrition is the major environmental factor regulating the concentration and composition of fat in ruminant milk. Feeding low-fibre/high-starch diets and/or lipid supplements rich in polyunsaturated fatty acids induce milk fat depression (MFD) in the bovine, typically increase milk fat secretion in the caprine, whereas limited data in sheep suggest that the responses are more similar to the goat than the cow. Following the observation that reductions in milk fat synthesis during diet-induced MFD are associated with increases in the concentration of specific trans fatty acids in milk, the biohydrogenation theory of MFD was proposed, which attributes the causal mechanism to altered ruminal lipid metabolism leading to increased formation of specific biohydrogenation intermediates that exert anti-lipogenic effects. Trans-10, cis-12 conjugated linoleic acid (CLA) is the only biohydrogenation intermediate to have been infused at the abomasum over a range of experimental doses (1.25 to 14.0 g/day) and shown unequivocally to inhibit milk fat synthesis in ruminants. However, increases in ruminal trans-10, cis-12 CLA formation do not explain entirely diet-induced MFD, suggesting that other biohydrogenation intermediates and/or other mechanisms may also be involved. Experiments involving abomasal infusions (g/day) in lactating cows have provided evidence that cis-10, trans-12 CLA (1.2), trans-9, cis-11 CLA (5.0) and trans-10 18:1 (92.1) may also exert anti-lipogenic effects. Use of molecular-based approaches have demonstrated that mammary abundance of transcripts encoding for key lipogenic genes are reduced during MFD in the bovine, changes that are accompanied by decrease in sterol response element binding protein 1 (SREBP1) and alterations in the expression of genes related to the SREBP1 pathway. Recent studies indicate that transcription of one or more adipogenic genes is increased in subcutaneous adipose tissue in cows during acute or chronic MFD. Feeding diets of similar composition do not induce MFD or substantially alter mammary lipogenic gene expression in the goat. The available data suggests that variation in mammary fatty acid secretion and lipogenic responses to changes in diet composition between ruminants reflect inherent interspecies differences in ruminal lipid metabolism and mammary specific regulation of cellular processes and key lipogenic enzymes involved in the synthesis of milk fat triacylglycerides.Keywords: milk fat, trans fatty acids, gene expression, lipogenesis, ruminants ImplicationsUnderstanding the regulation of milk fat synthesis is central to the development of nutritional strategies to enhance the nutritional value of milk, decrease milk-energ...

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Milk fat globules: Fatty acid composition, size and in vivo regulation of fat liquidity

Cited by 154 publications

References 22 publications

Adverse physicochemical properties of tripalmitin in beta cells lead to morphological changes and lipotoxicity in vitro

Adverse physicochemical properties of tripalmitin in beta cells lead to morphological changes and lipotoxicity in vitro

Relationships between milks differentiated on native milk fat globule characteristics and fat, protein and calcium compositions

Role of trans fatty acids in the nutritional regulation of mammary lipogenesis in ruminants

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