Effect of kolaviron on islet dynamics in diabetic rats

Abstract

Kolaviron, a biflavonoid isolated from the edible seeds of Garcinia kola, lowers blood glucose in experimental models of diabetes; however, the underlying mechanisms are not yet fully elucidated. The objective of the current study was to assess the effects of kolaviron on islet dynamics in streptozotocin-induced diabetic rats. Using double immunolabeling of glucagon and insulin, we identified insulin-producing β- and glucagon-producing α-cells in the islets of diabetic and control rats and determined the fractional β-cell area, α-cell area and islet number. STZ challenged rats presented with islet hypoplasia and reduced β-cell area concomitant with an increase in α-cell area. Kolaviron restored some islet architecture in diabetic rats through the increased β-cell area. Overall, kolaviron-treated diabetic rats presented a significant (p < 0.05) increase in the number of large and very large islets compared to diabetic control but no difference in islet number and α-cell area. The β-cell replenishment potential of kolaviron and its overall positive effects on glycemic control suggest that it may be a viable target for diabetes treatment.

Keywords: Diabetes; Garcinia kola; Islets; Kolaviron; α-cell; β-cell.

Fig. 1

Chemical structure of the bioactive compounds in Kolaviron – a Garcinia biflavonoid complex.

Fig. 2

The effect of kolaviron on glucose level in diabetic and non-diabetic rats over a 6-week treatment period. Data are presented as means ± S.D. Confirmation of diabetes (COD); Non-diabetic control (C), control treated with kolaviron (C + KV), untreated diabetic rats (D), diabetic rats treated with kolaviron (D + KV). * p < 0.05 compared to non-diabetic control rats, ^# p < 0.05 compared to diabetic control rats.

Fig. 3

Pancreata immunostained for glucagon-positive α-cells (brown staining) and insulin-positive β-cells (pink staining). Non-diabetic control (C), control treated with kolaviron (C + KV), untreated diabetic rats (D), diabetic rats treated with kolaviron (D + KV). Magnification X20.

Fig. 4

Total islet number, β-cell and α- cell area. Data are presented as means ± S.D. * p < 0.05 compared to non-diabetic control rats, ^#p < 0.05 compared to diabetic control rats. Non-diabetic control (C), control treated with kolaviron (C + KV), untreated diabetic rats (D), diabetic rats treated with kolaviron (D + KV).

Fig. 5

Size distribution of islets in rats. Size distribution of small-medium islets (0–12,500 µm) and large-very large islets (12,501 – >20,000 µm) in normal and diabetic rats. Data are presented as means ± S.D. * p < 0.05 compared to non-diabetic control rats, ^# p < 0.05 compared to diabetic control rats. Non-diabetic control rats (Black), non-diabetic control rats treated with kolaviron (Grey), untreated diabetic rats (Deep blue), diabetic rats treated with kolaviron (Light blue).