Organic cation transporter 1 variants and gastrointestinal side effects of metformin in patients with Type 2 diabetes.

AIMS: Metformin is the most widely used oral anti-diabetes agent and has considerable benefits over other therapies, yet 20-30% of people develop gastrointestinal side effects, and 5% are unable to tolerate metformin due to the severity of these side effects. The mechanism for gastrointestinal side effects and their considerable inter-individual variability is unclear. We have recently shown the association between organic cation transporter 1 (OCT1) variants and severe intolerance to metformin in people with Type 2 diabetes. The aim of this study was to explore the association of OCT1 reduced-function polymorphisms with common metformin-induced gastrointestinal side effects in Type 2 diabetes. METHODS: This prospective observational cohort study included 92 patients with newly diagnosed Type 2 diabetes, incident users of metformin. Patients were genotyped for two common loss-of-function variants in the OCT1 gene (SLC22A1): R61C (rs12208357) and M420del (rs72552763). The association of OCT1 reduced-function alleles with gastrointestinal side effects was analysed using logistic regression. RESULTS: Forty-three patients (47%) experienced gastrointestinal adverse effects in the first 6 months of metformin treatment. Interestingly, the number of OCT1 reduced-function alleles was significantly associated with over two-fold higher odds of the common metformin-induced gastrointestinal side effects (odds ratio = 2.31, 95% confidence interval 1.07-5.01, P = 0.034). CONCLUSIONS: In conclusion, we showed for the first time the association between OCT1 variants and common metformin-induced gastrointestinal side effects. These results confirm recent findings related to the role of OCT1 in severe metformin intolerance, and suggest that high inter-individual variability in mild/moderate and severe gastrointestinal intolerance share a common underlying mechanism. These data could contribute to more personalized and safer metformin treatment.

Effects of melatonin receptor 1B gene variation on glucose control in population from Bosnia and Herzegovina.

Common variants in MTNR1B, encoding melatonin receptor 1B, have been recently associated with impaired glucose homeostasis and an increased risk for developing Type 2 diabetes (T2D). In this study we investigated the association of MTNR1B variant rs10830963 with T2D and related quantitative traits in a population from Bosnia and Herzegovina (BH). A total number of 268 subjects were recruited in the study (162 T2D patients and 106 nondiabetic controls). Subjects were genotyped for MTNR1B rs10830963 SNP by using hydrolysis probes. Our data showed that the prevalence of the MTNR1B rs10830963 risk G-allele in BH population was 26%. Furthermore, we demonstrated a significant association of MTNR1B rs10830963 variant with fasting plasma glucose (FPG) levels in nondiabetic subjects. Under the additive genetic model, each variant G-allele was associated with an increased FPG levels of 0.29 mmol/L (95% CI 0.12, 0.46, p = 0.001). Strikingly, our results also showed a significant association of this MTNR1B polymorphism with increased glycated hemoglobin (HbA1c) levels in nondiabetic subjects (p = 0.040, additive genetic model). An association of the MTNR1B variant rs10830963 with T2D risk was not detected in our cohort. In conclusion, here we have demonstrated the association between the common MTNR1B rs10830963 variation and fasting plasma glucose levels in BH population. Furthermore, the influence of this polymorphism on the HbA1c levels was also shown in this study, further strengthening its role in blood glucose control.

Antioxidant and pro-oxidant capacity of catecholamines and related compounds. Effects of hydrogen peroxide on glutathione and sphingomyelinase activity in pheochromocytoma PC12 cells: potential relevance to age-related diseases.

The antioxidant and pro-oxidant capacity of catecholamines (CA) and related compounds were analyzed using the oxygen radical absorbance capacity (ORAC) assay. In the assay 2,2'-azobis (2-amidino-propane) dihydrochloride (AAPH), a peroxyl radical generator, ROO*; H2O2-Cu2+, mainly a hydroxyl radical generator, *OH; and Cu2+ a transition metal were used. The antioxidant effect of CA and its related compounds were in the order: neurotransmitters: dopamine (DA), norepinephrine (NE) > metabolites > amino acid precursors as measured by using AAPH. The antioxidant effect of CA and related compounds as measured by using AAPH were linearly correlated with concentration, while the antioxidant effect of CA in scavenging *OH produced by H2O2-Cu2+ increased proportionally to concentration at low concentration, but after reaching a maximum declined with increasing concentration. In the presence of Cu2+, CA acted as pro-oxidant. Glutathione (GSH) acted as a pro-oxidant when H2O2-Cu2+ or when Cu2+ alone was used as an oxidant and showed much higher pro-oxidant effect than DA, which could have relevance in the vulnerability of dopaminergic neurons to oxidative stress in the aging and aging related diseases. The antioxidant capacity of CA and many related compounds seems to be correlated with the numbers of hydroxyl groups and their position on the benzoic ring. The O-methylation and sulfate conjugation of the hydroxyl substitution inactivates both the antioxidant and pro-oxidant activities of CA. Our results show that oxidative stress induced by low (5 microM) or high (300 microM) doses H2O2 in pheochromocytoma PC12 cells significantly up-regulate the activity of Mg-dependent neutral sphingomyelinase (Sase), and significantly decreased GSH.

Influence of fluoxetine on regional serotonin synthesis in the rat brain.

The aim of the present study was to test the hypothesis that there should be a difference between the effects of an acute and an 8-day (chronic) administration of fluoxetine (10 mg/kg) on the rate of serotonin [5-hydroxytryptamine (5-HT)] synthesis. The 5-HT synthesis rate was measured in discrete regions of the rat brain using the alpha-[14C]methyl-L-tryptophan autoradiographic method. The results show that the acute and chronic fluoxetine treatments influence the 5-HT synthesis rate in different ways. A single dose of fluoxetine induced a significant increase in 5-HT synthesis in the visual, auditory, and parietal cortices, substantia nigra, hypothalamus, ventral thalamus, and dorsal hippocampus. In contrast, after a chronic treatment a decrease was observed in the substantia nigra, caudate, and nucleus accumbens, the auditory, parietal, sensorimotor, and frontal cortices, and ventral tegmental area. A significant decrease in the rate of 5-HT synthesis was observed in the dorsal raphe after both the single and chronic treatments. The results suggest that extracellular 5-HT has a delayed influence on the brain 5-HT synthesis rate in structures with serotonergic terminals. The findings from the acute study could be important for patients who have just started receiving fluoxetine treatment, as an increase in the 5-HT synthesis rate might occur in the acute phase of their treatment. In addition, the findings, from the chronic treatment study might give us a better understanding of how the brain serotonergic system adapts during a prolonged exposure to extracellular 5-HT.

The rate of valine incorporation into proteins with correction for valine recycling, measured in two brain tumor models and the cortex.

The tissue dilution factor (lambda) for the incorporation of valine into proteins in the rat cortex and in two different tumors, AA ascites and C6 glioma, was determined from measurements of specific activities in the tissue acid-soluble and aminoacyl-tRNA pools and in the plasma. A constant plasma specific activity was achieved by a constant infusion rate of [3H] valine. The data showed that the lambda for valine was the same in the cortex as in the tumors, and the recycling was approximately 36%. There was no difference in the lambda calculated on the basis of the specific activities in the tissue acid-soluble or aminoacyl-tRNA pools. The average dilution factor was found to be 0.64+/-0.05. The rate of valine incorporation into proteins was on average 3.2+/-0.4 and 4.9+/-0.4 nmol/g/min in the cortex for the groups of rats used in the AA ascites and C6 glioma experiments, respectively. In the AA ascites tumor the rate was approximately 41 and 29 nmol/g/min 4 and 7 days after tumor implantation, respectively, whereas in the C6 glioma the rate was approximately 41 and 72 nmol/g/min 6 and 13 days after inoculation, respectively. The tumors had, in comparison with the cortex, a significantly greater volume of distribution of valine. The amounts of valyl-tRNA were significantly greater in the tumors as compared with the normal cortex, with the exception of the glioma 6 days after implantation where the concentration was the same as in the cortex.

Histochemical aspects and fine structural characteristics of thyreocytes in pinealectomized and melatonin treated rats prior to irradiation.

The authors were investigating the histochemical and electron microscopic characteristics of thyreocytes in pinealectomized rats treated with melatonin, prior to irradiation. They observed that the animals that did not receive melatonin show a higher degree of the destruction appearing at the level of all ultrastructural organelles and a very low expression of the DNA and RNA histochemical reaction. These results suggest the role of melatonin in the determination of the thyreocyte behaviour under given irradiation conditions.