**4. Discussion**

242 Apoptosis and Medicine

antibody, DAB staining. Magnification: х400.

**E.** Streptozotocin-nicotinamide-induced diabetes **Figure 3.** TRAIL expression in pancreatic islet cells under different experimental diabetes conditions, day 14 (Streptozotocin-induced diabetes, day 7), splenic segment of the pancreas. TRAIL primary

**A.** Intact control **B.** Alloxan-induced diabetes

**C.** Streptozotocin-induced diabetes **D.** Immune-dependent diabetes

It is known that type I diabetes develops when pancreatic β-cells are damaged due to certain inflammatory, autoimmune and other pathological processes. Selective organ-specific tissue destruction of the insulin-producing pancreatic β-cells is associated with insulin deficiency resulting in impairment of glucose homeostasis. A large body of experimental evidence emphasizes the key role of apoptosis in the pathogenesis of diabetes mellitus (Kim B.M. et al. 2001; Severgina E.S. 2002; Butler A.E. et al. 2003; Bertalli E. et al. 2005; Rees D.A., et al. 2005; Srinivasan K., et al. 2007; Islam S., et al. 2009; Pisarev V.B. et al. 2009). Toxic effects of certain chemicals (e.g. alloxan, streptozotocin, etc.) used to induce diabetes specifically in pancreatic β-cells, manifest themselves by alkylation of DNA and formation of toxic compounds, such as superoxide anion, peroxynitrite, and nitric oxide. Damage to DNA and intracellular structures causes necrosis and activates apoptosis of pancreatic β-cells (Daisy Mythili M., et al. 2004).

Selective toxicity of streptozotocin can be explained by destruction of antiradical protective system and pancreatic β-cell DNA fragmentation. Numerous experiments show that the principal cause of streptozotocin-induced β-cell death is alkylation of DNA. Exposure of cells to streptozotocin results in the formation of toxic compounds, such as superoxide anion, peroxynitrite, and nitric oxide (NO). However, the contribution of NO to the cytotoxic activity remains controversial, because low concentrations of NO in the cells inhibit the inducible forms of NO-synthase, thus reducing DNA fragmentation (Szkudelski T. 2001; Lenzen S. 2008).

Receptor- or mitochondrial-mediated pathway may trigger programmed pancreatic β-cell death (Szkudelski T. 2001). Induction of β-cell apoptosis can occur through a TRAILmediated mechanism. DNA damage can activate p53 gene which regulates the expression of DR5 and/or DR4 death receptors, thus enhancing TRAIL-induced apoptosis (Haupt S., et al. 2003; Kelley R.F., et al. 2005). Our studies provide evidence for activation of TRAIL-induced apoptosis in pancreatic β-cells by administration of streptozotocin on models of streptozotocin-induced and immune-dependent diabetes.

Pancreatic Islet Beta-Cell Apoptosis in Experimental Diabetes Mellitus 245

M.P. Voronkova

**5. References** 

**Acknowledgement** 

*Department of Pharmacology, Volgograd State Medical University, Russia* 

Journal of Clinical Biochemistry Vol. 22. №2. pp.60-64

Histochem. & Cytochem. Vol.53. N3. pp.1071-1086

Sci. Vol. 116. N 20. pp.4077-85

Biol Chem. Vol. 280. N 3. pp.2205-12

3. pp.85-90

12. pp.2192-2202

[3] Baranov V.G. (1983) Experimental diabetes mellitus. Leningrad

cardiac myocyte apoptosis. Circ Res. Vol. 95. N 10. pp.957-70

Methods Find Exp. Clin. Pharmacol. Vol. 4. N31. pp.249-261

We express our gratitude to the Head of pharmacology department of Volgograd State Medical University, Academician of Russian Academy for Medical Sciences, Honored Scientist of Russia, MD, full professor, Spasov Alexander A., assistant professor of pharmacology department of Volgograd State Medical University, PhD, Cheplyaeva Natalia I., assistant professor of pharmacology department of Volgograd State Medical University,

[1] Akbarzadeh A., et al. (2007) Induction of diabetes by streptozotocin in rats. Indian

[2] Allred D.C., Harvey J.M., Berardo M., Clark G.M. (1998) Prognostic and predictive factors in breast cancer by immunohistochemical analysis. Mod. Pathol.11. pp.155-68

[4] Bertalli E., Bendayan M. (2005) Association between endocrine pancreas and ductal system. More than an epiphenomenon of endocrine differentiation and development? J.

[5] Butler A.E., Janson J., Bonner-Weir S., et al. (2003) β-cell deficit and increased β-cell

[6] Crow M.T., Mani K., Nam Y.J., et. al. (2004) The mitochondrial death pathway and

[7] Daisy M., Rashmi V., Akila G., Gunasekaran S. (2004) Effect of streptozotocin on the ultrastructure of rat pancreatic islets. Microsc. Res. Tech. Vol.63. N 5. pp.274 – 281 [8] Haupt S., Berger M., Goldberg Z., Haupt Y. (2003) Apoptosis - the p53 network. J. Cell

[9] Islam S., Loots D.T. (2009) Experimental rodent models of type 2 diabetes: a review.

[10] Jung J.Y., Kim W.J. (2004) Involvement of mitochondrial- and Fas-mediated dual mechanism in CoCl(2)-induced apoptosis of rat PC12 cells. Neurosci Lett. Vol. 371. N 2-

[11] Kelley R.F., Totpal K., Lindstrom S.H., et al. (2005) Receptor-selective mutants of Apo2L/TRAIL reveal a greater contribution of DR5 than DR4 to apoptosis signaling. J

[12] Kim B.M., Ham Y.M., Shin Y.J., et al. (2001) Clusterin expression during regeneration of pancreatic islet β-cell in streptozotocin-induced diabetic rats. Diabetologia. Vol. 44. N

[13] Korzhevsky A. (2005) Summary of the foundations of histological techniques for

doctors, laboratory technicians as well as histologists. St. Petersburg

apoptosis in humans with type 2 diabetes. Diabetes Vol. 52. N1.pp.102-110

PhD, Chepurnova Mariya V. for their assistance in conducting the present study.

Mitochondrial-mediated apoptotic pathway plays an important role in the development of pancreatic islet damage in diabetes mellitus (Sakurai K., et al. 2001). In alloxan-induced diabetes intracellular calcium homeostasis is typically impaired. *In vitro* and *in vivo* experiments have shown that cytoplasmic calcium concentrations increase in the cells of pancreatic islets. This effect is due to depolarization of cell and mitochondrial membranes of βendocrine cells which is associated with excessive entry of calcium from the extracellular fluid and intracellular calcium mobilization (Crow M.T., et al. 2004; Jung J.Y., et al. 2004). Thus, considerable gross damage to the intracellular structures by free radicals, oxidation of SHproteins and impairment of intracellular calcium homeostasis typically result in necrosis and apoptosis, with necrotic processes being more common in alloxan-induced diabetes.

Comparison of morphological data and the dynamics of impairment of β-cell functional activity in experimental models (alloxan-, streptozotocin-, nicotinamide-streptozotocininduced and immune-dependent diabetes) gives insight into the pathogenesis of experimental diabetes. A high apoptotic index and the prevalence of destructive processes, which enable us to assess not only the extent of pancreatic tissue damage but also to evaluate biochemical parameters, such as plasma glucose, insulin, C-peptide, etc., can be used as markers of severity of experimental diabetes (Snigur G.L., Smirnov A.V. 2010).

Thus, apoptosis is a complex, multi-step, poorly regulated process. Any regulatory impairment can lead to the development of pathological changes in the endocrine apparatus of pancreatic islets including the development of experimental diabetes (Reed J.C., Green D.R. 2011). Each level and element of this system is a potential drug target. The significance of apoptosis determines the need for the refocusing of biomedical research from theoretical biology to clinical medicine. Investigation of apoptotic mechanisms in various pathological conditions enable us to make more accurate diagnoses and prognoses as well as to adjust therapy. The possibility of deliberate control of apoptotic processes is considered to be the basis for developing new medications used to treat many socially important diseases, including the development of anti-diabetic drugs.

Experimental diabetic rats exhibited significant pathohistological changes in the pancreatic islets caused by cytotoxine (streptozotocin+CFA) at all levels of tissue structure. The development of diabetes mellitus was associated with decreased volume fraction of pancreatic islets and β-cells due to inflammation (insulitis) and pronounced destructive changes (e.g. necrosis and apoptosis).
