Insulin modulates the strong reinforcing effects of nicotine and changes in insulin biomarkers in a rodent model of diabetes

The influence of high-fat diet on nicotine vapor self-administration, neuronal excitability, and leptin levels in adult mice

With the rise in fast-food culture and the continued high numbers of tobacco-related deaths, there has been a great deal of interest in understanding the relationship between high-fat diet (HFD) and nicotine use behaviors. Using adult mice and a patch-clamp electrophysiology assay, we investigated the influence of HFD on the excitability of ventral tegmental area (VTA) dopamine neurons and pyramidal neurons in the medial prefrontal cortex (mPFC) given their role in modulating the reinforcing effects of nicotine and natural rewards. We then examined whether HFD-induced changes in peripheral markers were associated with nicotine use behaviors. Here, mice were assigned standard diet (SD) or HFD for 6 weeks and then trained to self-administer nicotine using an e-vape® self-administration (EVSA) assay. After the last session, changes in glucose, insulin, and leptin were assessed with ELISA. HFD-assigned mice displayed a decrease in intrinsic excitability of VTA dopamine neurons; but an increase in intrinsic excitability of layer VI prelimbic mPFC neurons. SD-assigned female mice demonstrated enhanced nicotine EVSA during fixed-ratio 3 relative to SD males. HFD-assigned male and female mice displayed increased nicotine EVSA during FR1. However, only HFD-assigned male mice exhibited enhanced nicotine EVSA during FR3. Finally, HFD-assigned male and female mice displayed increased leptin levels. However, we only observed a direct correlation between leptin levels and EVSA responding during FR1 in HFD-fed male mice. These results suggest that high-fat diet alter nicotine intake in a sex-specific manner, and this may be due to diet-induced changes in neuronal excitability and circulating leptin levels.

Effectiveness of pharmacotherapies for diabetes on nicotine, food, and water intake in insulin-resistant rats

The intersectionality between diabetes medications and nicotine consumption was assessed in female and male rats. Briefly, the rats were fed a high-fat diet (HFD) or regular diet (RD) for 4 weeks. Then separate groups received vehicle or a low dose of streptozotocin (STZ; 25 mg/kg). Three days later, insulin resistance was assessed by measuring plasma glucose levels for 180 min following an injection of insulin (0.75 U/kg). The rats were then prepared with jugular catheters, and they were given 23 h access to nicotine intravenous self-administration (IVSA) in 4 days cycles with 3 days of forced abstinence in their home cages where they consumed their respective diet. During the IVSA sessions, operant responses for food and water and changes in body weight were recorded. Prior to administration of the pharmacotherapies, the rats were given access to two doses of nicotine (0.015 then 0.03 mg/kg for the remainder of the study). Then, daily injections of the pharmacotherapies were given at the onset of dark cycle (6 p.m.) in the following order: 1) dapagliflozin (3.0 then 10.0 mg/kg), 2) insulin (0.75 U/kg twice), and 3) bromocriptine (3.0 then 10.0 mg/kg). The results suggest that our HFD+STZ regiment induced insulin resistance in female and male rats. Also, the HFD-fed rats displayed higher nicotine intake than RD controls, regardless of sex. Administration of insulin, but not dapagliflozin or bromocriptine, normalized nicotine intake in HFD-fed rats to control levels. These results have clinical implications regarding the potential efficacy of insulin to control excessive nicotine intake in persons with diabetes.

The emergence of insulin resistance following a chronic high-fat diet regimen coincides with an increase in the reinforcing effects of nicotine in a sex-dependent manner

The present study assessed the sex-dependent effects of insulin resistance on the reinforcing effects of nicotine. Female and male rats received a chronic high-fat diet (HFD) or regular diet (RD) for 8 weeks. A subset of rats then received vehicle or a dose of streptozotocin (STZ; 25 mg/kg) that induces insulin resistance. To assess insulin resistance, glucose levels were measured 15, 30, 60, 120, and 180 min after an insulin injection (0.75 U/kg). Nine days later, the rats were given extended access to intravenous self-administration (IVSA) of nicotine (0.015, 0.03, 0.06 mg/kg) in an operant box where they consumed their respective diet ad libitum and performed responses for water deliveries. Each nicotine dose was delivered for 4 days with 3 intermittent days of abstinence in their home cage. The day after the last IVSA session, physical signs were compared following administration of mecamylamine (3.0 mg/kg) to precipitate nicotine withdrawal. The results revealed that there were no changes in insulin resistance or nicotine intake in HFD alone rats regardless of sex. Insulin resistance was observed in HFD-fed rats that received STZ, and the magnitude of this effect was greater in males versus females. Our major finding was that nicotine intake was greater among HFD + STZ female rats as compared to males. Lastly, the physical signs of withdrawal were similar across all groups. Our results suggest that females diagnosed with disorders that disrupt insulin signaling, such as diabetes may be at risk of greater vulnerability to nicotine use due to enhanced reinforcing effects of this drug.

Vitamin D3 attenuates oxidative stress and regulates glucose level and leukocyte count in a semi-chronic streptozotocin-induced diabetes model

Purpose

Vitamin D3 (vit-D3) is a potent immunomodulator with anti-inflammatory and antioxidative properties. We used streptozotocin (STZ)-induced rat model of diabetes (DM) to evaluate the effects of vit-D3. We measured serum biochemical parameters, interleukin-17 (IL-17), osteocalcin (OC), malondialdehyde (MDA), and immune cell count on the 21st day of experiment.

Method

A total of 24 Wistar rats were randomly divided into three groups. Each group had eight rats. During the 1st day of the experiment, the control group was injected intraperitoneally with citrate buffer, while STZ group and STZ + vit-D3 group were injected by a single i.p. dose (35 mg/kg) of STZ dissolved in citrate buffer (pH 4,5; 0,1 M). Vitamin D3 was applied via oral gavage once daily to the STZ + vit-D3 group for a total period of 14 days, starting from the 7th day of the experiment.

Results

STZ rats showed a significant reduction in OC and an increase in MDA and IL-17 serum concentrations compared to the control rats. We also observed a significant STZ-associated decrease in the number of lymphocytes and a significant increase in monocyte and eosinophil number. Oral treatment with vit-D3 to STZ-induced diabetic rats significantly increased OC and decreased MDA serum levels. Furthermore, vit-D3 treatment resulted in a good regulation of hematopoiesis such as increase in the number of segmented granulocytes and lymphocytes and a reduction in the number of monocytes and eosinophils.

Conclusion

Vit-D3 treatment has important therapeutic effects; among many others it can attenuate oxidative stress and ameliorate the hyperglycemic state in the STZ-induced rat diabetic model, which is promising for further clinical trials.

Insulin restores the neurochemical effects of nicotine in the mesolimbic pathway of diabetic rats

This study examined whether insulin modulates the neurochemical effects of nicotine in the mesolimbic pathway of diabetic rats. The rats received vehicle or streptozotocin (STZ) to induce hypoinsulinemia. A subset of STZ-treated rats was implanted with insulin pellets that rapidly normalized glucose levels. Two-weeks later, dialysis probes were implanted into the nucleus accumbens (NAc) and ipsilateral ventral tegmental area (VTA). The next day, dialysate samples were collected during baseline and then following systemic administration of nicotine. Samples were also collected following intra-VTA administration of the gamma-aminobutyric acid (GABA)A receptor antagonist, bicuculline. Dopamine, GABA, glutamate, and acetylcholine (ACh) levels were assessed using liquid chromatography/mass spectrometry (LC/MS). The results revealed that vehicle-treated rats displayed a nicotine-induced increase in NAc dopamine levels. In contrast, STZ-treated rats did not display any changes in NAc dopamine following nicotine administration, an effect that was likely related to a concomitant increase in GABA and decrease in glutamate levels in both the NAc and VTA. Intra-VTA administration of bicuculline increased NAc dopamine in vehicle-treated rats, and this effect was absent in STZ-treated rats. Vehicle-treated rats displayed a nicotine-induced increase in ACh levels in the NAc (but not VTA), an effect that was lower in the NAc of STZ-treated rats. Insulin supplementation normalized the neurochemical effects of nicotine in the NAc and VTA of STZ-treated rats, suggesting that insulin modulates the neurochemical effects of nicotine in the mesolimbic pathway of diabetic rats.

Examination of nicotine and saccharin reward in the Goto-Kakizaki diabetic rat model

Morbidity and mortality attributed to type 2 diabetes have exponentially increased in the US. At exceptionally high risk is a subpopulation of persons with type 2 diabetes who smoke, which are shown to have decreased success rates of smoking cessation than euglycemic smokers. Preclinical research in our laboratory has shown that the rewarding effects of nicotine are enhanced in the streptozotocin and high-fat diet rodent model of diabetes. It is presently unclear whether this enhancement of nicotine reward can be demonstrated in other insulin resistant rat models. This study aimed to determine if a similar increase in nicotine reward is found in Goto-Kakizaki (GK) rats, a model of the spontaneous formation of insulin resistance in an inbred sub-strain of Wistar rat. Nicotine conditioned place preference (CPP) was examined in Sprague-Dawley (SD), Wistar, and GK rats. A robust nicotine CPP was found in SD and Wistar rats, but nicotine CPP was not detected in GK rats. Locomotor activity was also evaluated in all three strains, and GK rats demonstrated significantly less activity as compared to SD and Wistar rats. To further assess reward behavior in GK rats, consumption of saccharin solution was measured over a 48 -h period. GK rats showed a significant increase in saccharin intake compared to SD rats. These findings suggest that GK rats experience an enhanced hedonic processing as compared to SD rats. The lack of nicotine CPP in GK rats may be due to deficits in learning and memory, thus hindering their ability to acquire or express a place preference.

Chronic Tobacco Exposure by Smoking Develops Insulin Resistance

BACKGROUND AND OBJECTIVES

The present review critically discusses the high occurrence rate, insulin resistance and type-2 diabetes in tobacco exposed individuals. Tobacco extracts and smoke contain a large number of toxic materials and a significant number of those are metabolic disintegrators.

DISCUSSION

Glucose and lipid homeostasis is severely impaired by this compound. Tobacco exposure contributes to adverse effects by impairing the physical, biochemical and molecular mechanisms in the tissues. The immunological components are damaged by tobacco with high production of proinflammatory cytokines (IL-6, TNF-∞) and augmentation of inflammatory responses. These events result in damages to cytoskeletal structures of different tissues. Degradation of matrix structure (by activation of different types of MMPs) results in the permanent damages to the tissues and their metabolic functions. Cellular antioxidant defense system mostly cannot or hardly nullify CS-induced ROS production that activates polymorphonuclear neutrophils (PMNs), which are a major source of cytokines and chemokines (TNFα, IL6, IL8, INFγ). Additive effects of these immediately promote the low energy-metabolism as well as inflammation. Oxidative stress, mitochondrial dysfunction, and inflammation contribute to the direct nicotine toxicity via nAChRs in diabetes. The investigator identified that skeletal muscle insulin-resistance occurs in smokers due to phosphorylation of insulin receptor substrate1 (IRS1) at Ser-636 position.

CONCLUSION

Tobacco exposure initiates free radical related immunological impairment, DNA damage, and inflammation. So, the present analysis is of importance to figure out the mechanistic layout of tobacco-induced tissue damage and its possible therapeutic interventions.

The influence of tobacco smoke exposure on selected markers of oxidative stress, kidneys and liver function in the serum of rats with streptozotocin-induced diabetes

BACKGROUND

The significance of the free radicals is emphasized in the pathophysiology of diabetes and the progression of chronic diabetic complications. Smoking cigarettes increases the risk of developing type II diabetes and intensifies pathophysiological processes during the development of type I diabetes. Tobacco smoke is also additional source of free radicals. Moreover, smoking causes variety of adverse effects on organs, that have no direct contact with the tobacco smoke itself. The objective of the study was to examine the effects of tobacco smoke on the serum concentrations of relevant oxidative stress markers such as total protein (TP), reduced glutathione (GSH), glutathione S-transferase (GST) and thiobarbituric acid reactive substances (TBARS), as well as renal (creatinine, urea) and liver function (alkaline phosphatase, ALP; alanine aminotransferase, ALT; aspartate aminotransferase, AST) among animals with induced diabetes after administration of a single dose of streptozotocin (65 mg/kg, ip).

METHODS

The markers of oxidative stress and biochemical parameters were determined using spectrophotometric methods. As a biomarker of exposure to tobacco smoke, cotinine was determined using high-performance liquid chromatography with diode array detection (HPLC-DAD).

RESULTS

Tobacco smoke exposure of diabetic rats was manifested by significantly elevated liver enzymes activity - ALT (p < 0.05) and ALP (p < 0.01), higher creatinine and urea concentration (p < 0.01), lower GSH amount (p < 0.05), and higher GST activity (p < 0.05).

CONCLUSIONS

Tobacco smoking induce liver and renal damage through the mechanisms including increased oxidative stress.