Effect of quercetin on brain protein kinase C-alpha expression and serotonin level in streptozotocin-induced diabetic rats

Hyperglycemia is a key factor in diabetic complications. However, the mechanism of hyperglycemia-induced brain changes remains poorly understood. The aim of the present study was to investigate the effect of diabetes on serotonin [5-hydroxytryptamine; 5-HT] levels and protein kinase C-alpha [PKC-alpha] expression in brain. The potential protective effect of quercetin [QE]; as phytochemical on diabetic brain was additionally studied. This study was carried out on 60 adult male albino rats divided into three main groups; group I [control] included 20 vehicle-treated rats, group II [diabetic] consisted of 20 rats injected once intraperitonially with streptozotocin [STZ; 50mg/kb body weight] amid group III [insulin-treated diabetic] comprised 20 diabetic rats injected subcutaneously with insulin [SIU/kg/day]. Each group was subdivided into 2 subgroups; subgroup I [non-QE treated] and subgroup 2[QE-treated]. QE was administered orally [10mg/kg/day]. At the end of the implemental period, all rats were sacrificed, blood samples were withdrawn and their brains were rapidly removed and dissected. 5-HT was extracted from brain samlples and their concentrations were estimated fluorophotometrically. PKC-alpha expression was quantitated by immunoblot from extracted brain samples. The STZ-induced diabetic rats showed significant marked hyperglycemia and higher brain PKC-alpha expression as compared to both control and insulin-treated diabetic groups. However, brain 5-HT concentrations did not differ significantly between the three studied groups. Only in diabetic rats, QE administration produced a significant increase in 5-HT concentrations and a decrease in PKC-alpha expression but with no effect on blood glucose levels. A highly significant direct correlation was found between blood glucose and PKC-alpha expression levels. However, 5-HT did not correlate with either blood glucose or PKC-alpha expression. it could be concluded that STZ-induced chronically hyperglycemic rats were associated with enhanced PKC-alpha expression as well as unaltered neurotransmitter; 5-HT in brain. QE seems to act perfectly in diabetic rats by mechanisms other than antihyperglycemic action. The neuroprotective effect of QE in diabetics was suggested to be through both elevating 5-HT and lowering PKC-alpha expression. Consequently, controlling hyperglycemia is still the most essential approach for primary prevention of diabetic complications

Cell type-specific upregulation of myristoylated alanine-rich C kinase substrate and protein kinase C-alpha, -beta I, -beta II, and -delta in microglia following kainic acid-induced seizures

Myristoylated alanine-rich C kinase substrate (MARCKS) is a widely distributed protein kinase C (PKC) substrate and has been implicated in actin cytoskeletal rearrangement in response to extracellular stimuli. Although MARCKS was extensively examined in various cell culture systems, the physiological function of MARCKS in the central nervous system has not been clearly understood. We investigated alterations of cellular distribution and phosphorylation of MARCKS in the hippocampus following kainic acid (KA)-induced seizures. KA (25 mg/kg, i.p.) was administered to eight to nine week-old C57BL/6 mice. Behavioral seizure activity was observed for 2 h after the onset of seizures and was terminated with diazepam (8 mg/kg, i.p.). The animals were sacrificed and analyzed at various points in time after the initiation of seizure activity. Using double-labeling immunofluorescence analysis, we demonstrated that the expression and phosphorylation of MARCKS was dramatically upregulated specifically in microglial cells after KA-induced seizures, but not in other types of glial cells. PKC alpha, beta I, beta II and delta, from various PKC isoforms examined, also were markedly upregulated, specifically in microglial cells. Moreover, immunoreactivities of phosphorylated MARCKS were co-localized in the activated microglia with those of the above isoforms of PKC. Taken together, our in vivo data suggest that MARCKS is closely linked to microglial activation processes, which are important in pathological conditions, such as neuroinflammation and neurodegeneration.