Pancreastatin inhibitor PSTi8 protects the obesity associated skeletal muscle insulin resistance in diet induced streptozotocin-treated diabetic mice

Pancreastatin inhibitor PSTi8 improves ovarian health in Letrozole-HFD induced PCOS rats by ameliorating metabolic and reproductive parameters

Polycystic ovary syndrome (PCOS) is a heterogeneous endocrine and metabolic disorder associated with insulin resistance (IR) and hyperandrogenism. IR plays a crucial role in the etiology of PCOS. An insulin-sensitizing agent like metformin is most commonly used as an off-label drug for the treatment of PCOS. PSTi8 (a pancreastatin inhibitor) is known as a promising therapeutic insulin-sensitizing agent for the treatment of IR in metabolic diseases. Thus, this study evaluates the insulin-sensitizing effects of PSTi8 compared to metformin on IR, hyperandrogenism, ovarian, and metabolic dysfunction in a PCOS model. To induce PCOS, rats were administered letrozole at a dose of 2 mg/kg via oral administration and fed a 60 % high-fat diet. Metformin and PSTi8 lowered serum insulin, testosterone, luteinizing hormone (LH) levels, and the LH/follicle-stimulating hormone ratio in the blood serum and improved steroidogenic gene expression in the PCOS ovaries. Both treatments increased the levels of sex hormone-binding globulin and estrogen hormone. Metformin and PSTi8 restore ovarian and uterine histomorphometry and improve the estrous cycle in PCOS rats. Metformin and PSTi8 treatments also improve blood glucose level and increase insulin sensitivity, inflammation, reactive oxygen species accumulation, lipid parameters, body weight, and fat mass in PCOS rats. This study revealed that PSTi8 is as helpful as metformin in decreasing hyperandrogenism by improving insulin sensitivity, free testosterone level and restoring disturbed reproductive and metabolic parameters in PCOS rats. PSTi8 has potential to serve as a therapeutic molecule for preventing IR induced by a western diet in PCOS.

Protective Effects of Exogenous Melatonin Administration on White Fat Metabolism Disruption Induced by Aging and a High-Fat Diet in Mice

Obesity has emerged as a major risk factor for human health, exacerbated by aging and changes in dietary habits. It represents a significant health challenge, particularly for older people. While numerous studies have examined the effects of obesity and aging on fat metabolism independently, research on their combined effects is limited. In the present study, the protective action against white fat accumulation after a high-fat diet (HFD) exerted by exogenous melatonin, a circadian hormone endowed with antioxidant properties also involved in fat metabolism, was investigated in a mouse model. For this purpose, a battery of tests was applied before and after the dietary and melatonin treatments of the animals, including epididymal white adipose tissue (eWAT) histological evaluations, transcriptomic and lipidomic analyses, real-time PCR tests, immunofluorescence staining, Western blot, the appraisal of serum melatonin levels, and transmission electron microscopy. This study found that aged mice on a high-fat diet (HFD) showed increased lipid deposition, inflammation, and reduced antioxidant glutathione (GSH) levels compared to younger mice. Lipidomic and transcriptomic analyses revealed elevated triglycerides, diglycerides, ceramides, and cholesterol, along with decreased sphingomyelin and fatty acids in eWAT. The genes linked to inflammation, NF-κB signaling, autophagy, and lipid metabolism, particularly the melatonin and glutathione pathways, were significantly altered. The aged HFD mice also exhibited reduced melatonin levels in serum and eWAT. Melatonin supplementation reduced lipid deposition, increased melatonin and GSH levels, and upregulated AANAT and MTNR1A expression in eWAT, suggesting that melatonin alleviates eWAT damage via the MTNR1A pathway. It also suppressed inflammatory markers (e.g., TNF-α, NLRP3, NF-κB, IL-1β, and CEBPB) and preserved mitochondrial function through enhanced mitophagy. This study highlights how aging and HFD affect lipid metabolism and gene expression, offering potential intervention strategies. These findings provide important insights into the mechanisms of fat deposition associated with aging and a high-fat diet, suggesting potential intervention strategies.

Chromogranin A-derived peptides pancreastatin and catestatin: emerging therapeutic target for diabetes

Chromogranin A (ChgA) is an acidic pro-protein found in neuroendocrine organs, pheochromocytoma chromaffin granules, and tumor cells. Proteolytic processing of ChgA gives rise to an array of biologically active peptides such as pancreastatin (PST), vasostatin, WE14, catestatin (CST), and serpinin, which have diverse roles in regulating cardiovascular functions and metabolism, as well as inflammation. Intricate tissue-specific role of ChgA-derived peptide activity in preclinical rodent models of metabolic syndrome reveals complex effects on carbohydrate and lipid metabolism. Indeed, ChgA-derived peptides, PST and CST, play a pivotal role in metabolic syndrome such as obesity, insulin resistance, and diabetes mellitus. Additionally, supplementation of specific peptide in ChgA-KO mice have an opposing effect on physiological functions, such as PST supplementation reduces insulin sensitivity and enhances inflammatory response. In contrast, CST supplementation enhances insulin sensitivity and reduces inflammatory response. In this review, we focus on the tissue-specific role of PST and CST as therapeutic targets in regulating carbohydrate and lipid metabolism, along with the associated risk factors.

Immuno-metabolic effect of pancreastatin inhibitor PSTi8 in diet induced obese mice: In vitro and in vivo findings

AIMS

Pancreastatin (PST), an anti-insulin peptide derived from chromogranin A. Its levels increase in cases of obesity, which contributes to adipose tissue inflammation and insulin resistance. This study aims to investigate the immunometabolic effect of PST inhibitor (PSTi8) against PST by using in vitro and in vivo finding.

MAIN METHODS

3T3-L1 cells were differentiated with or without PSTi8, and Oil Red O staining was performed. J774A.1 cells were used for macrophage polarization study. The diet-induced obesity and T2DM model was developed in C57BL/6 mice through high-fat diet for 8 weeks. Alzet osmotic pumps were filled with PSTi8 (release rate: 2 mg/kg/day) and implanted in mice for eight weeks. Further, insulin and glucose tolerance tests were performed. Liver and eWAT sections were stained with hematoxylin and eosin. FACS was used to measure mitochondrial ROS and membrane potential, while Oroboros O2k was used to measure oxygen consumption rate. Immunocytochemistry and qRT-PCR were done for protein and gene expression, respectively.

KEY FINDINGS

PSTi8 inhibited the expression of lipolytic genes and proteins in 3T3-L1 adipocytes. PSTi8 improved the inulin sensitivity, lipid profile, MMP, and OCR levels in the 3T3-L1 adipocyte and eWAT. It also increased the M1 to M2 macrophage polarization in J77A.1 cells and eWAT. Further, PSTi8 attenuated inflammatory CD4⁺ T, CD8⁺ T cells and increased the anti-inflammatory T-reg and eosinophil populations in the eWAT. It also reduced the expression of pro-inflammatory genes like Mcp1, Tnfα, and Il-6.

SIGNIFICANCE

Collectively, PSTi8 exerted its beneficial effect on adipose tissue inflammation and restored energy expenditure against diet-induced obesity.

Pancreastatin inhibitor PSTi8 prevents free fatty acid-induced oxidative stress and insulin resistance by modulating JNK pathway: In vitro and in vivo findings

AIM

Free fatty acid-mediated obesity plays a crucial role in the pathogenesis of Type 2 Diabetes. FFA induced JNK activation acts as a central regulator in causing hepatic insulin resistance. Similarly, Pancreastatin, a chromogranin A peptide, serves as a crucial link between FFA-induced insulin resistance. Therefore, in the present work, we sought to test Pancreastatin inhibitor PSTi8 to ameliorate FFA-induced hepatic insulin resistance in in vitro and in vivo models.

MATERIAL AND METHODS

To verify our objective, we exposed hepatocytes (HepG2 cells) with palmitate (0.3 mM) or palmitate + PSTi8 (200 nM). Parallelly mice were fed either HFD or HFD + PSTi8 (1 mg/kg). After 21 days animals were scanned for increased fat mass, along with GTT, ITT and PTT experiment to check glucose, and insulin tolerance. Furthermore, ROS generation and hepatic glycogen content was measured in FFA exposed hepatocytes. Gene expression and protein expression studies were further conducted to delineate the action mechanism of PSTi8.

KEY FINDINGS

PSTi8 exposure decreased ROS accumulation, lipid accumulation, and reduced glycogen content in FFA-induced groups. It also enhances glucose uptake and reduces gluconeogenesis to combat the FFA effect. Furthermore, gene expression studies indicate that PSTi8 treatment reduces NADPH oxidase3 (NOX3) expression and inhibits JNK signaling, a predominant source of ROS-induced insulin resistance.

SIGNIFICANCE

To summarize, the protective effect of PSTi8 on FFA-induced insulin resistance is mediated via inhibition of JNK signaling, which leads to decreased ROS generation and enhanced insulin sensitivity. Hence PSTi8 could be a therapeutic molecule to prevent western diet-induced insulin resistance.

Evaluation of the Pharmacokinetics of the Pancreastatin Inhibitor PSTi8 Peptide in Rats: Integration of In Vitro and In Vivo Findings

PSTi8 is a pancreastatin inhibitory peptide that is effective in the treatment of diabetic models. This study investigates the pharmacokinetic (PK) properties of PSTi8 in Sprague Dawley rats, for the first time. In vitro and in vivo PK studies were performed to evaluate the solubility, stability in plasma and liver microsomes, plasma protein binding, blood-plasma partitioning, bioavailability, dose proportionality, and gender difference in PK. Samples were analyzed using the validated LC-MS/MS method. The solubility of PSTi8 was found to be 9.30 and 25.75 mg/mL in simulated gastric and intestinal fluids, respectively. The protein binding of PSTi8 was estimated as >69% in rat plasma. PSTi8 showed high stability in rat plasma and liver microsomes and the blood-plasma partitioning was >2. The bioavailability of PSTi8 after intraperitoneal and subcutaneous administration was found to be 95.00 ± 12.15 and 78.47 ± 17.72%, respectively, in rats. PSTi8 showed non-linear PK in dose proportionality studies, and has no gender difference in the PK behavior in rats. The high bioavailability of PSTi8 can be due to high water solubility and plasma protein binding, low clearance and volume of distribution. Our in vitro and in vivo findings support the development of PSTi8 as an antidiabetic agent.

Role and function of granin proteins in diabetes mellitus

The granin glycoprotein family consists of nine acidic proteins; chromogranin A (CgA), chromogranin B (CgB), and secretogranin II-VIII. They are produced by a wide range of neuronal, neuroendocrine, and endocrine cells throughout the human body. Their major intracellular function is to sort peptides and proteins into secretory granules, but their cleavage products also take part in the extracellular regulation of diverse biological processes. The contribution of granins to carbohydrate metabolism and diabetes mellitus is a recent research area. CgA is associated with glucose homeostasis and the progression of type 1 diabetes. WE-14, CgA10-19, and CgA43-52 are peptide derivates of CgA, and act as CD4+ or CD8+ autoantigens in type 1 diabetes, whereas pancreastatin (PST) and catestatin have regulatory effects in carbohydrate metabolism. Furthermore, PST is related to gestational and type 2 diabetes. CgB has a crucial role in physiological insulin secretion. Secretogranins II and III have angiogenic activity in diabetic retinopathy (DR), and are novel targets in recent DR studies. Ongoing studies are beginning to investigate the potential use of granin derivatives as drugs to treat diabetes based on the divergent relationships between granins and different types of diabetes.

The Emerging Roles of Chromogranins and Derived Polypeptides in Atherosclerosis, Diabetes, and Coronary Heart Disease

Chromogranin A (CgA), B (CgB), and C (CgC), the family members of the granin glycoproteins, are associated with diabetes. These proteins are abundantly expressed in neurons, endocrine, and neuroendocrine cells. They are also present in other areas of the body. Patients with diabetic retinopathy have higher levels of CgA, CgB, and CgC in the vitreous humor. In addition, type 1 diabetic patients have high CgA and low CgB levels in the circulating blood. Plasma CgA levels are increased in patients with hypertension, coronary heart disease, and heart failure. CgA is the precursor to several functional peptides, including catestatin, vasostatin-1, vasostatin-2, pancreastatin, chromofungin, and many others. Catestatin, vasostain-1, and vasostatin-2 suppress the expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in human vascular endothelial cells. Catestatin and vasostatin-1 suppress oxidized low-density lipoprotein-induced foam cell formation in human macrophages. Catestatin and vasostatin-2, but not vasostatin-1, suppress the proliferation and these three peptides suppress the migration in human vascular smooth muscles. Chronic infusion of catestatin, vasostatin-1, or vasostatin-2 suppresses the development of atherosclerosis of the aorta in apolipoprotein E-deficient mice. Catestatin, vasostatin-1, vasostatin-2, and chromofungin protect ischemia/reperfusion-induced myocardial dysfunction in rats. Since pancreastatin inhibits insulin secretion from pancreatic β-cells, and regulates glucose metabolism in liver and adipose tissues, pancreastatin inhibitor peptide-8 (PSTi8) improves insulin resistance and glucose homeostasis. Catestatin stimulates therapeutic angiogenesis in the mouse hind limb ischemia model. Gene therapy with secretoneurin, a CgC-derived peptide, stimulates postischemic neovascularization in apolipoprotein E-deficient mice and streptozotocin-induced diabetic mice, and improves diabetic neuropathy in db/db mice. Therefore, CgA is a biomarker for atherosclerosis, diabetes, hypertension, and coronary heart disease. CgA- and CgC--derived polypeptides provide the therapeutic target for atherosclerosis and ischemia-induced tissue damages. PSTi8 is useful in the treatment of diabetes.

Pancreastatin mediated regulation of UCP-1 and energy expenditure in high fructose fed perimenopausal rats

AIMS

Pancreastatin (PST) is a crucial bioactive peptide derived from chromogranin A (CHGA) proprotein that exhibits an anti-insulin effect on adipocytes. Herein, we investigated the effects of PST on brown adipose tissues (BAT) and white adipose tissue (WAT) in connection with uncoupling protein-1 (UCP-1) regulated energy expenditure in high fructose diet (HFrD) fed and vinylcyclohexenediepoxide (VCD) induced perimenopausal rats.

MATERIAL AND METHODS

We administered VCD in rats for 17 consecutive days and fed HFrd for 12 weeks. After 12 weeks estradiol and progesterone levels were detected. Furthermore, detection of glucose tolerance, insulin sensitivity, and body composition revealed impaired glucose homeostasis and enhanced PST levels. Effects of enhanced PST on UCP-1 level in BAT and WAT of perimenopausal rats were further investigated.

KEY FINDINGS

Reduced serum estradiol, progesterone, and attenuated insulin response confirmed perimenopausal model development. Furthermore, enhanced PST serum level and its increased expression in BAT and WAT downregulated the UCP-1 expression. Subsequently, impaired ATP level, NADP/NADPH ratio, citrate synthase activity, enhanced mitochondrial reactive oxygen species (ROS) generation and perturbed mitochondrial membrane potential, further exacerbated mitochondrial dysfunction, cellular ROS production, and promoted apoptosis. Interestingly, PST inhibition by PST inhibitor peptide-8 (PSTi8) displayed a favorable impact on UCP-1 and energy expenditure.

SIGNIFICANCE

The aforementioned outcomes indicated the substantial role of PST in altering the UCP-1 expression and associated energy homeostasis. Hence our results corroborate novel avenues to unravel the quest deciphering PST's role in energy homeostasis and its association with perimenopause.

PSTi8 with metformin ameliorates perimenopause induced steatohepatitis associated ER stress by regulating SIRT-1/SREBP-1c axis

Aims

Hepatic steatosis in women confronting menopause is the manifestation of substantial fructose consumption and forms a positive feedback loop to develop endoplasmic reticulum (ER) stress. Previously pancreastatin inhibitor peptide-8 (PSTi8) and Metformin (Met) combination effectively ameliorated hepatic lipid accumulation in high fructose diet (HFrD) fed diabetic mice models at reduced doses. Moreover, SIRT-1 plays a crucial role in the regulation of SREBP-1c. Hence we hypothesized that Met and PSTi8 in combination (at therapeutic lower doses) could mitigate hepatic steatosis linked ER stress by activating SIRT-1 and precluding SREBP-1c in HFrD fed 4-Vinylcyclohexenediepoxide (HVCD) induced perimenopausal rats.

Main methods

HVCD rats were fed HFrD for 12 weeks, accompanied by 14 days of treatment with Met, PSTi8, and combination. We confirmed model establishment by estrus cycle study, estradiol level, and intraperitoneal glucose tolerance test. Plasma lipid profile and liver function were determined. Also, mRNA and protein expressions were examined. Moreover, distribution of SIRT-1 and SREBP-1c was detected in HepG2 cells by immunofluorescence staining.

Key findings

HVCD group displayed augmented insulin resistance (IR), lipogenesis, and ER stress in the liver. Combination therapy improved the estrus cyclicity, estradiol, and lipid profile of HVCD rats. Met and PSTi8 combination reduced hepatic SREBP-1c and triggered SIRT-1 expression in high fructose-induced insulin-resistant HepG2 cells; consequently, combination therapy attenuated ER stress.

Significance

Succinctly, present research promotes impetus concerning the remedial impact of Met with PSTi8 at lower therapeutic doses to ameliorate hepatic IR, steatosis, and associated ER stress by revamping the SIRT-1/SREBP-1c axis in perimenopausal rats.

Combination of Pancreastatin inhibitor PSTi8 with metformin inhibits Fetuin-A in type 2 diabetic mice

In the preceding study, we delineated that high-fat diet (HFD) consumption in mice increases the circulatory level of pancreastatin (PST), which additionally enhances the free fatty acid (FFA) concentration in circulation. Consequently, the aggravated FFA activates Fetuin-A, which facilitates hepatic lipid accumulation, insulin resistance (IR), and culminates in type 2 diabetes (T2D). Metformin (Met) is a widely known first-line drug for the treatment of T2D. We previously unveiled PSTi8, an inhibitor of PST, comprising antidiabetic property. Hence, we hypothesized that combination therapy of Met and PSTi8, at reduced therapeutic doses, would mitigate HFD-induced IR by inhibiting hepatic Fetuin-A in mice model of T2D. C57BL/6 mice were fed HFD for 12 weeks, followed by treatment with Met, PSTi8, and its combination for 10 days. Glucose and insulin tolerance tests were conducted. Circulatory levels of PST, Fetuin-A, and lipid markers were determined. Also, the mRNA and protein expression of Fetuin-A was assessed by qPCR, western blotting, and immunofluorescence. Moreover, the energy expenditure was measured by comprehensive laboratory animal monitoring system (CLAMS). Combination therapy displayed improved PST, Fetuin-A, and lipid profile in plasma. We also found reduced hepatic Fetuin-A, which reduced inhibitory phosphorylation of IRS and increased phosphorylation of AKT. Consequently, ameliorated hepatic lipogenesis, gluconeogenesis, and inflammation. Also, combination treatment attenuated Fetuin-A expression, lipid accumulation, and glucose production in palmitate-induced HepG2 cells. Altogether current study promulgates the beneficial effect of combination therapy of Met and PSTi8 (comparable to alone higher therapeutic doses) to ameliorate Fetuin-A activation, hepatic lipid accumulation, insulin resistance, and associated progressive pathophysiological alterations in T2D.