Mechanism of action of somatostatin in pancreatic β-cells: oxidative metabolism, glycolysis pathway and role of extracellular calcium influx

The mechanism of action of somatostatin (SRIF) has been extensively studied during the last five decades since the discovery of the peptide in 1974. However, there are many concealed actions of the peptide to control insulin secretion from pancreatic β–cells. This can contribute to resolving the dilemmas of cancer and diabetes mellitus. To achieve this goal, the MIN6 cell line was used as a model of insulin secreting pancreatic β-cells. Polarographic oxygen and enzymatic lactate electrodes were used to measure oxygen consumption rate (OCR) and lactate production rate, respectively. Imaging techniques were used to measure the mitochondrial membrane potential (ΔΨmit) using Rhodamine 123 (Rh123) dye and Ca2+ influx using Fluo-4 probe. Glucose uptake and ATP production were measured by Promega® plate-based assays, the Glucose Uptake-Glo™ Assay, and CellTiter-Glo® 2.0 Assay, respectively. 100 nM SRIF significantly and equally inhibited OCR stimulated by both 10 mM glucose and 10 mM α-ketoisocaproate (KIC); this effect was not seen in the absence of substrates. 10 mM glucose significantly decreased basal Rh123 fluorescence, the effect was reversed by 100 nM SRIF. In Ca2+ free condition, 100 nM SRIF did not affect ΔΨmit while it depolarized ΔΨmit in the presence of nifedipine. The peptide had no effect on ATP production either in the presence or in the absence of each mitochondrial fuels. It neither affected the glucose uptake nor the glucokinase activity in MIN6 cells. The peptide also inhibited lactate production in the absence and presence of 1 µM cyclosporine A (CSA) but not in the presence of each 100 nM okadaic acid (OKA) or ethanol. SRIF decreased the basal and substrate-induced Ca2+ influx into MIN6, the effect was abolished by pre-incubation of the cells with pertussis toxin (PTX). 1 µM dibutyryl cAMP significantly decreased the inhibitory action of SRIF. In conclusion, SRIF inhibited glycolysis and mitochondrial metabolism but not glucose uptake nor ATP production. This indicates that the inhibitory effect of the peptide on plasma membrane electrical activity was not due to inhibition of metabolism. It is also concluded that SRIF effectively inhibited Ca2+ influx into MIN6 cells directly via blocking VGCCs and indirectly by activation of K+ channels conductance. The inhibitory action of the peptide is achieved via a PTX sensitive pathway, and it is a cAMP-independent mechanism

Role of anti-inflammatory interleukin 10 in asymptomatic heartworm infection (Dirofilariasis) in dogs

Background: Dirofilaria immitis causes heartworm disease (HWD), a vector-borne zoonotic disease that primarily affects dogs and cats. Occasionally, human beings were reported to be infected as well. The current study aims to discover the asymptomatic dirofilariasis infection in dogs. In addition, to determine the prevalence of heartworm disease and the role of anti-inflammatory interleukin 10 (IL10) in developing the disease. Household dogs were selected from 10 veterinary clinics throughout Basrah, south of Iraq.Methods: The study included 117 dogs older than 12 months, none of them had received heartworm vaccinations, and all of them lived in their owners’ houses for at least 9 months. Animal ethics instructions were followed after the owner’s consent was obtained.  Physical and biochemical examinations were conducted including the examination of circulating antigens of microfilaria. The levels of anti-inflammatory IL10 and pro-inflammatory IL17, IL4, and IFN-γ were measured using ELISA tests. Descriptive statistics were used to evaluate the prevalence and the clinical and immunological results of the study.Results: Canine heartworm disease prevalence was 29.05% (34 out of 117). The physical examination showed normal vital signs for both infected and non-infected dogs. A significant elevation in the total WBC count was noticed in the infected group.  On the other hand, a significant decrease in RBCs count and hemoglobin was found in the infected group. There were neither changes in the platelet count nor the liver enzymes concentration between infected and non-infected groups.  A significant increase in anti-inflammatory interleukin 10 level and a significant decrease in pro-inflammatory IL17, IL4, and IFN-γ were noticed in the infected dogs. Conclusion: It is concluded that dirofilariasis infection is considered to be a serious life-threatening disease for dogs in Iraq. Therefore, a periodic test for heartworm infection every six months is recommended to eradicate heartworm infestations. The infected animals must be treated according to the American Heartworm Association recommendations

Mechanism of action of somatostatin in pancreatic β-cells: oxidative metabolism, glycolysis pathway and role of extracellular calcium influx

The mechanism of action of somatostatin (SRIF) has been extensively studied during the last five decades since the discovery of the peptide in 1974. However, there are many concealed actions of the peptide to control insulin secretion from pancreatic β–cells. This can contribute to resolving the dilemmas of cancer and diabetes mellitus. To achieve this goal, the MIN6 cell line was used as a model of insulin secreting pancreatic β-cells. Polarographic oxygen and enzymatic lactate electrodes were used to measure oxygen consumption rate (OCR) and lactate production rate, respectively. Imaging techniques were used to measure the mitochondrial membrane potential (ΔΨmit) using Rhodamine 123 (Rh123) dye and Ca2+ influx using Fluo-4 probe. Glucose uptake and ATP production were measured by Promega® plate-based assays, the Glucose Uptake-Glo™ Assay, and CellTiter-Glo® 2.0 Assay, respectively. 100 nM SRIF significantly and equally inhibited OCR stimulated by both 10 mM glucose and 10 mM α-ketoisocaproate (KIC); this effect was not seen in the absence of substrates. 10 mM glucose significantly decreased basal Rh123 fluorescence, the effect was reversed by 100 nM SRIF. In Ca2+ free condition, 100 nM SRIF did not affect ΔΨmit while it depolarized ΔΨmit in the presence of nifedipine. The peptide had no effect on ATP production either in the presence or in the absence of each mitochondrial fuels. It neither affected the glucose uptake nor the glucokinase activity in MIN6 cells. The peptide also inhibited lactate production in the absence and presence of 1 µM cyclosporine A (CSA) but not in the presence of each 100 nM okadaic acid (OKA) or ethanol. SRIF decreased the basal and substrate-induced Ca2+ influx into MIN6, the effect was abolished by pre-incubation of the cells with pertussis toxin (PTX). 1 µM dibutyryl cAMP significantly decreased the inhibitory action of SRIF. In conclusion, SRIF inhibited glycolysis and mitochondrial metabolism but not glucose uptake nor ATP production. This indicates that the inhibitory effect of the peptide on plasma membrane electrical activity was not due to inhibition of metabolism. It is also concluded that SRIF effectively inhibited Ca2+ influx into MIN6 cells directly via blocking VGCCs and indirectly by activation of K+ channels conductance. The inhibitory action of the peptide is achieved via a PTX sensitive pathway, and it is a cAMP-independent mechanism