Inhibitory Effect of Crocin(s) on Lens α-Crystallin Glycation and Aggregation, Results in the Decrease of the Risk of Diabetic Cataract

Abstract

The current study investigates the inhibitory effect of crocin(s), also known as saffron apocarotenoids, on protein glycation and aggregation in diabetic rats, and α-crystallin glycation. Thus, crocin(s) were administered by intraperitoneal injection to normal and streptozotocin-induced diabetic rats. The cataract progression was recorded regularly every two weeks and was classified into four stages. After eight weeks, the animals were sacrificed and the parameters involved in the cataract formation were measured in the animal lenses. Some parameters were also determined in the serum and blood of the rats. In addition, the effect of crocin(s) on the structure and chaperone activity of α-crystallin in the presence of glucose was studied by different methods. Crocin(s) lowered serum glucose levels of diabetic rats and effectively maintained plasma total antioxidants, glutathione levels and catalase activity in the lens of the animals. In the in vitro study, crocin(s) inhibited α-crystallin glycation and aggregation. Advanced glycation end products fluorescence, hydrophobicity and protein cross-links were also decreased in the presence of crocin(s). In addition, the decreased chaperone activity of α-crystallin in the presence of glucose changed and became close to the native value by the addition of crocin(s) in the medium. Crocin(s) thus showed a powerful inhibitory effect on α-crystallin glycation and preserved the structure-function of this protein. Crocin(s) also showed the beneficial effects on prevention of diabetic cataract.

Keywords: cataract; crocin(s); glycation; oxidative stress; streptozotocin; structure-function.

Figure 1

Non-tryptophan AGE fluorescence of α-crystallin (Cry), in the presence of 500 mM of glucose (Glc) with and without crocin(s) (C).

Figure 2

ANS fluorescence of α-crystallin, in the presence of 500 mM of glucose with and without crocin(s).

Figure 3

(A) Far-UV CD spectra of α-crystallin, in the presence of 500 mM of glucose with and without crocin(s); (B) Electrophoretic mobility of α-crystallin. M, Molecular Marker, 1-3, α-crystallin alone, in the presence of glucose and glucose+crocin(s), respectively.

Figure 4

Chaperone activity of α-crystallin as measured by the suppression of heat-induced aggregation of catalase. Catalase was incubated at 60 °C in the absence and presence of native α-crystallin and in the presence of α-crystallin with glucose or glucose+crocin(s).

Figure 5

Changes in the body weight of all rat groups during the time course of the study.

Figure 6

Changes in the (A): glucose concentration; (B): percent of HbA1c; (C): fluorescence intensity of AGEs; and (D): FRAP, in different groups of rats at the beginning (0 week), middle (4 weeks), and at the end (8 weeks) of the experiment. “a” indicates the significance of the data that compares group N vs. all groups. “b” indicates the significance of the data that compares group D vs. groups of crocin(s)-treated rats. *, p < 0.05; #, p < 0.01; and †, p < 0.001.

Figure 7

Change in the opacity of the lenses in different group of rats. N, Normal; D, diabetic; DC and NC, diabetic and normal rats received crocin(s).