Long-term streptozotocin diabetes impairs arachidonic and docosahexaenoic acid metabolism and ∆5 desaturation indices in aged rats
Introduction
Polyunsaturated fatty acids (PUFAs) are basic structural components of cell membranes, and their content in the phospholipid bilayer influences the membrane's fluidity and selective permeability (Tosi et al., 2014). They are precursors for inflammatory factors, and act as signaling molecules in cells (Raza Shaikh and Brown, 2013). Hence, their alteration could result in different pathological changes in tissues (Tosi et al., 2014). There is a large amount of evidence about the role of PUFA balance in the development of senile changes in the nervous and musculoskeletal systems, and the beneficial effects of their supplementation on degenerative changes during aging (Denis et al., 2013, Lukiw and Bazan, 2008, Pepe, 2005).
The regulation of bioconversion of PUFA from their precursors involves the activity of desaturase enzymes (Δ9D, Δ6D, Δ5D), elongases (Elovl2, Elovl4, Elovl5, Elovl6) and transcription factors, such as peroxisome proliferator-activated receptors (PPARδ, PPARγ, PPARα) and sterol response element-binding protein-1c (SREBP-1c) (Tu et al., 2010). These rate-limiting enzymes and transcription factors can be influenced by various nutritional, hormonal, physiological and genetic factors.
In insulin dependent diabetes mellitus (IDDM) PUFA bioconversion is significantly altered with the decrease in mRNA expression of Δ9 desaturase (Montanaro et al., 2005), Δ6 desaturase (Comte et al., 2004, Rimoldi et al., 2001) and Δ5 desaturase (Montanaro et al., 2005). The impairment of desaturase mRNA expression may be, at least partially, reversed by insulin treatment (Comte et al., 2004, Montanaro et al., 2005, Rimoldi et al., 2001). In streptozotocin (STZ) induced IDDM, elongase gene expression is also decreased, with organ specific characteristics (Tikhonenko et al., 2010). The expression of transcription factors such as PPARs is also changed (Huang et al., 2007, Son et al., 2007) and in some experiments insulin restores values to normal (Huang et al., 2007). The most consistent changes in the fatty acid composition of different tissues in IDDM experimental rats include: a decrease in palmitic acid (Chanussot et al., 1997, Comte et al., 2004, Ghebremeskel et al., 2002, Malaisse et al., 2006) and a decrease in monounsaturated fatty acids (MUFA) (Comte et al., 2004, Montanaro et al., 2005). Other important changes are not consistent and include a decrease in 20:4n6 and/or increase in its precursors (18:2n6 and 20:3n6), and an unusual increase in 22:6n3 (Brenner, 2003).
There are many reports about lipid metabolism changes in the tissues of diabetic rats during short-term studies. Since diabetes mellitus (DM) is a chronic disease, this study quantified long-term changes in total lipid and phospholipid metabolism in the tissues of diabetic rats during aging.
Section snippets
Animals and diets
The experimental protocol was approved by the Veterinary Directorate of the Ministry of Agriculture of the Republic of Croatia and the Ethical Committee of the Veterinary Faculty, University of Zagreb. Male, 2-month old, Sprague–Dawley rats (Animal Husbandry Unit of the University of Split, Split, Croatia), weighing 160 to 180 g, were randomly divided into four groups of 8 animals each and fed with certified laboratory rat feed (4RF21 GLP, Mucedola, Settimo Milanese, Italy) (Table 1). The access
Results
Successful induction of diabetes was confirmed in experimental rats by measurement of blood glucose levels. As expected, glycemia was strongly increased in STZ groups (Fig. 1). The state of IDDM was confirmed with blood glucose values > 16.5 mmol/l. All the rats that received streptozotocin developed IDDM, with the exception of one rat from the DM 12 group (excluded from the experiment). Final average body weights were: 380, 256, 461 and 305 g for the CON 6, DM 6, CON 12 and DM 12 groups,
Discussion
The present study was performed to investigate the consequences of long-term IDDM on fatty acid composition and desaturation indices in the tissues of aging rats. A period of 12 months was taken to observe the effects of chronic, long-term diabetes because dynamic changes in long-term diabetes require continuous monitoring of the diabetic model after induction of diabetes (Bakovic et al., 2013). After an initial increase in C22:6n3 values in 6 month diabetic rats, we noticed a decrease in C22:6n3
Conclusions
In conclusion, numerous changes in fatty acid composition were observed in aged rats with long-term diabetes. Our results suggest that age could worsen the expected decrease in MUFA and C20:4n6 synthesis in IDDM. Moreover, long-term diabetes could impair C22:6n3 synthesis in the liver and muscle, and incorporation of C22:6n3 and C20:4n6 into brain phospholipids. These substantial changes could be involved in the pathogenesis of senile and diabetes-induced damage. In light of the increasing age
Conflict of interest
All authors decline conflicts of interests.
Acknowledgments
The study was funded by the Ministry of Science, Education and Sports, Republic of Croatia grant no. 053-0532265-2244 awarded to Zeljko Mikulec and the Croatian Foundation for Science (HRZZ) grant no. 02.05./28 awarded to Livia Puljak.
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