Abstract
Cinnamon Extract (CE) has shown to be generally safe when ingested and to have many pharmacological properties. Problem statement: Study the effects of daily intake of CE on the modulation of hepatic, cardiac Insulin Receptor Substrate-1 (IRS-1) and their relations to some inflammatory variables in hyperinsulinemic rats. Approach: The influence of CE administered orally was studied in hyperinsulinemic rats. Eighteen male Wistar rats were divided into 3 groups of 6 rats each. Group 1; control animals received starch as control diet, while Groups 2; rats were fed a "high-fructose diet" (60%). Group 3; fructose-fed rats received orally CE (0.5 mL/rat/day) from the 16th day of fructose feeding in experimental period. The animals were maintained in their respective groups for 30 days. At the end of the experimental period, Serum levels of glucose, insulin, lipid profile, Total Antioxidant Capacity (TAC), Malondialdehyde (MDA), sialic acid and soluble Fas (sFas) were assayed. Hepatic and cardiac IRS-1 levels were also evaluated. Results: Fed high fructose diet to rats induced significant elevations in serum levels of glucose, insulin, triacylglycerol, HDL-c, sialic acid, sFas and MDA, while the level of serum TAC was significantly reduced as compared to controls. Also significant reduction in the levels of hepatic and cardiac IRS-1 were recorded as compared to controls. Oral administration of cinnamon extract to fructose-fed rats alleviated the effects of fructose and these rats showed a normal level of the parameters studied. The percentage changes of IRS-1 level in fructose-fed rats before and after treatment with CE were 38.51 for liver and 31.92% for cardiac muscle. This increase in IRS-1 level after treatment is still lowered than control level with the percentage change -11.82 and -9.93% for liver and cardiac muscle respectively. There was a significant positive correlation between IRS-1 and TAC level whereas there was negative correlation between IRS-1 and MDA, sialic acid and sFas. Conclusion: This study reports interest findings that cinnamon extract enhances glucose uptake by activating insulin receptor kinase activity in rats fed high fructose diet and it has additional roles as antioxidant and anti-inflammatory agents. Thus, clinical application of cinnamon could be considered as a potential therapeutic option in humans in the treatment of insulin resistance states. So inclusion of cinnamon in the daily diet could be recommended.
Highlights
It has been established that insulin resistance occurs in rats fed high fructose diet in which insulin actions were impaired
Various defects in insulin action have been reported in animals, the exact mechanisms involved in the insulin resistance have not been adequately defined (Carvalho et al, 1996)
The present results showed a state of moderate insulin resistance in fructose-fed rats, as demonstrated by significant elevation of serum glucose, insulin levels and higher value of Homeostasis Model Assessment (HOMA) index as compared with control fed rats
Summary
It has been established that insulin resistance occurs in rats fed high fructose diet in which insulin actions were impaired. Insulin initiates its metabolic and growth promoting effects by binding to α-subunit of its tetrameric receptors thereby activating the kinase in the β subunit This interaction catalyses the intramolecular autophosphorylation of specific tyrosine residues of the β subunit which farther enhances the tyrosine kinase activity of the receptor toward other protein substrates (White and Kahn, 1994). In most cells, this primary events leads to the subsequent tyrosyl phosphorylation to a cytoplasmic protein with an apparent molecular weight of 160-185 KDa, called insulin receptor substrate-1 (IRS-1) (Sun et al, 1991). Considerable evidence indicates that insulin receptor tyrosine kinase and associated IRS-1 phosphorylation are essential for many of the biological effects of insulin
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