The effect of Nateglinide and Octreotide on follicular morphology and free radical scavenging system in letrazole-induced rat model of PCOS.

OBJECTIVE: To investigate the effects of octreotide and nateglinide on ovarian follicle count, ovarian tissue damage, biochemical parameters and free radical scavenging system in letrazole-induced rat model of PCOS. MATERIALS AND METHODS: Forty-two female Sprague-Dawley rats were divided into six groups. Group 1 (Control Group): after localizing the ovaries and the uterine horns, the abdominal wall was closed without any surgical procedure. Group 2 (PCOS Group): PCOS was induced by administrating Letrozole orally for 21 successive days. At the end of 21 days, rats underwent ovarian biopsies. The experimental PCOS model was considered successful in the presence of atretic follicles without granulosa cell stratification. Group 3 (PCOS + Nateglinide Group): Nateglinide was administered by oral dropper for 30 days to the rats in which PCOS model was created. Group 4 (Nateglinid only Group): 30 days of NG was applied to the rats without PCOS. Group 5 (PCOS+Octreotide Group): 0.1 mg/kg/day Octreotide was given intraperitoneally for 4 weeks to the rats in which PCOS model was created. Group 6 (Octreotide only Group): animals without PCOS given 0.1 mg/kg/day Octreotide at the end of the treatment, bilateral oophorectomy was performed and blood samples were collected from all groups. Ovarian tissue was stained immunohistochemically with TLR-4 in addition to conventional staining. In addition to follicle classification, ovarian damage was graded. Serum insulin, FSH and LH, TNF-α, IL-6, SHBG, SOD, IGF-1, MDA and GSH levels were also measured. RESULTS: The cystic and degenerated follicle density of PCOS group was high compared with the other groups. Both cystic and degenerated follicles were significantly reduced in PCOS+NG and PCOS+OC groups compared to PCOS group. There was no difference between the groups in terms of serum LH, FSH and insulin levels (p>0.05). Serum testosterone level was significantly higher in the PCOS group compared to the other groups (p<0.01). Adding OC or NG to PCOS groups did not cause significant changes in testosterone levels. TNF-α and IL-6 levels were high in PCOS group (p<0.03). IGF-1 and MDA levels were higher in PCOS than in other groups (p<0.03, p<0.01 respectively). Adding OC or NG to the treatment normalized IGF-1 and MDA levels. Serum GSH levels were significantly lower in the PCOS group (p<0.05). Adding NG to the treatment increased GSH levels. CONCLUSIONS: Both NG and OCT reverses atretic and degenerate follicle damage due to PCOS through TLR-4, antioxidant and anti-inflammatory pathways.

The Nitrated Form of Nateglinide Induces Apoptosis in Human Pancreatic Cancer Cells Through a Caspase-dependent Mechanism.

BACKGROUND/AIM: Nitric oxide (NO) has antitumor activity against various solid tumor cell types in addition to its vasodilatory effect. In the current study, we investigated the effect and mechanism of the synthetic nitrated form (NO2-NAT) of nateglinide, a hypoglycemic agent, on the induction of cell death in human pancreatic cancer cells. MATERIALS AND METHODS: NO production was evaluated by measuring nitrite (NO2) and nitrate (NO3) (NOx). Apoptotic cell numbers were determined using annexin V. RESULTS: NO2-NAT released nitrate and nitrite ions immediately upon dissolving in aqueous solution. NO2-NAT caused significant extracellular leakage of lactate dehydrogenase (LDH) in the human pancreatic cancer cell lines AsPC1 and BxPC3, and increased annexin-positive cells in a time- and concentration-dependent manner. NO2-NAT also significantly increased the activity of caspases 3 and 7. Exposure to Z-VAD-FMK, a caspase inhibitor, significantly suppressed NO2-NAT-induced cell death. CONCLUSION: These results indicated that NO2-NAT induces apoptosis in human pancreatic cancer cells and may serve as a new NO-based chemotherapeutic agent for the treatment of pancreatic cancer.

Acute Peripheral Inflammation Increases Plasma Concentration of Hypoglycemic Agent Nateglinide with Decreased Hepatic Drug-Metabolizing Activity in Rats.

The effects of inflammation on hypoglycemic agents were evaluated in male rats with acute peripheral inflammation (API). Nateglinide (NTG) was utilized as a model compound, since it is a hepatically-metabolized compound and its metabolism is mainly mediated by CYP 2C11 enzyme. In the experiments, rats were subjected to carrageenan injection into their hind paws for API induction, and the plasma concentration profiles of NTG were then examined. In addition, pooled liver microsomes were prepared from control and API rats, and the hepatic drug-metabolizing activity toward NTG and the hepatic expression of CYP2C11 protein were evaluated. It was shown that the plasma concentration of NTG following its intravenous administration decreases at a slower rate in API rats than that in control rats. It was also indicated in the incubation study with the liver microsomes that the hepatic drug-metabolizing activity toward NTG decreases in API rats. Additionally, it was revealed in Western immunoblotting that the hepatic expression of CYP2C11 protein decreases in API rats. These findings suggest that inflammation occurring in peripheral tissues brings about a decrease in hepatic NTG metabolism by suppressing the hepatic expression of CYP2C11 protein, causing an alteration of the plasma concentration profile of NTG with its impaired elimination.

Nateglinide Exerts Neuroprotective Effects via Downregulation of HIF-1α/TIM-3 Inflammatory Pathway and Promotion of Caveolin-1 Expression in the Rat's Hippocampus Subjected to Focal Cerebral Ischemia/Reperfusion Injury.

Ischemic stroke is a major cause of death and motor disabilities all over the world. It is a muti-factorial disorder associated with inflammatory, apoptotic, and oxidative responses. Nateglinide (NAT), an insulinotropic agent used for the treatment of type 2 diabetes mellitus, recently showed potential anti-inflammatory and anti-apoptotic effects. The aim of our study was to elucidate the unique neuroprotective role of NAT in the middle cerebral artery occlusion (MCAO)-induced stroke in rats. Fifty-six male rats were divided to 4 groups (n = 14 in each group): the sham-operated group, sham receiving NAT (50 mg/kg/day, p.o) group, ischemia/reperfusion (IR) group, and IR receiving NAT group (50 mg/kg/day, p.o). MCAO caused potent deficits in motor and behavioral functions of the rats. Significant increase in inflammatory and apoptotic biomarkers has been observed in rats' hippocampi. Janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) pathway was significantly stimulated causing activation of series inflammatory biomarkers ending up neuro-inflammatory milieu. Pretreatment with NAT preserved rats' normal behavioral and motor functions. Moreover, NAT opposed the expression of hypoxia-inducible factor-1α (HIF-1α) resulting in downregulation of more inflammatory mediators namely, NF-κB, tumor necrosis factor-ß (TNF-ß), and the anti-survival gene PMAIP-1. NAT stimulated caveolin-1 (Cav-1) which prevented expression of oxidative biomarkers, nitric oxide (NO), and myeloperoxidase (MPO) and hamper the activation of apoptotic biomarker caspase-3. In conclusion, our work postulated that NAT exhibited its neuroprotective effects in rats with ischemic stroke via attenuation of different unique oxidative, apoptotic, and inflammatory pathways.

Impairment of Intestinal Monocarboxylate Transporter 6 Function and Expression in Diabetic Rats Induced by Combination of High-Fat Diet and Low Dose of Streptozocin: Involvement of Butyrate-Peroxisome Proliferator-Activated Receptor-γ Activation.

Generally, diabetes remarkably alters the expression and function of intestinal drug transporters. Nateglinide and bumetanide are substrates of monocarboxylate transporter 6 (MCT6). We investigated whether diabetes down-regulated the function and expression of intestinal MCT6 and the possible mechanism in diabetic rats induced by a combination of high-fat diet and low-dose streptozocin. Our results indicated that diabetes significantly decreased the oral plasma exposure of nateglinide. The plasma peak concentration and area under curve in diabetic rats were 16.9% and 28.2% of control rats, respectively. Diabetes significantly decreased the protein and mRNA expressions of intestinal MCT6 and oligopeptide transporter 1 (PEPT1) but up-regulated peroxisome proliferator-activated receptor γ (PPARγ) protein level. Single-pass intestinal perfusion demonstrated that diabetes prominently decreased the absorption of nateglinide and bumetanide. The MCT6 inhibitor bumetanide, but not PEPT1 inhibitor glycylsarcosine, significantly inhibited intestinal absorption of nateglinide in rats. Coadministration with bumetanide remarkably decreased the oral plasma exposure of nateglinide in rats. High concentrations of butyrate were detected in the intestine of diabetic rats. In Caco-2 cells (a human colorectal adenocarcinoma cell line), bumetanide and MCT6 knockdown remarkably inhibited the uptake of nateglinide. Butyrate down-regulated the function and expression of MCT6 in a concentration-dependent manner but increased PPARγ expression. The decreased expressions of MCT6 by PPARγ agonist troglitazone or butyrate were reversed by both PPARγ knockdown and PPARγ antagonist 2-chloro-5-nitro-N-phenylbenzamide (GW9662). Four weeks of butyrate treatment significantly decreased the oral plasma concentrations of nateglinide in rats, accompanied by significantly higher intestinal PPARγ and lower MCT6 protein levels. In conclusion, diabetes impaired the expression and function of intestinal MCT6 partly via butyrate-mediated PPARγ activation, decreasing the oral plasma exposure of nateglinide.

Niosomes for oral delivery of nateglinide: in situ-in vivo correlation.

Niosomes have been claimed to enhance intestinal absorption and to widen the absorption window of acidic drugs. This was reported after monitoring the intestinal absorption in situ. Accordingly, the aim of this work was to investigate the effect of niosomal encapsulation on intestinal absorption and oral bioavailability of nateglinide. This was conducted with the goal of correlation between in situ intestinal absorption and in vivo availability. The drug was encapsulated into proniosomes. The niosomes resulting after hydration of proniosomes were characterized with respect to vesicle size and drug entrapment efficiency. The in situ rabbit intestinal absorption of nateglinide was monitored from its aqueous solution and niosomes. Streptozotocin was used to induce diabetes in albino rats which were then used to assess the hypoglycemic effect of nateglinide after oral administration of aqueous dispersion and niosomal systems. The prepared vesicles were in the nanoscale with the recorded size being 283 nm. The entrapment efficiency depended on the pH of the formulation. The in situ intestinal absorption reflected non-significant alteration in the membrane transport parameters of the drug after niosomal encapsulation compared with the free drug solution. In contrast, niosomes showed significant improvement in the rate and extent of the hypoglycemic effect compared with the unprocessed drug. This discrepancy can be attributed to different transport pathway for the drug after niosomal inclusion with the vesicles undergoing translymphatic transport which can minimize presystemic metabolism. However, this requires confirmatory investigations. In conclusion niosomes can enhance oral bioavailability of nateglinide with the absorption being through nontraditional pathway.