Cytoprotective effects of polyenoylphosphatidylcholine (PPC) on beta-cells during diabetic induction by streptozotocin

Soybean polyenylphosphatidylcholine (PPC) is beneficial in liver and extrahepatic tissue injury: An update in experimental research

Polyenylphosphatidylcholine (PPC) is a purified polyunsaturated phosphatidylcholine extract of soybeans. This article updates PPC's beneficial effects on various forms of liver cell injury and other tissues in experimental research. PPC downregulates hepatocyte CYP2E1 expression and associated hepatotoxicity, as well as attenuates oxidative stress, apoptosis, lipoprotein oxidation and steatosis in alcoholic and nonalcoholic liver injury. PPC inhibits pro-inflammatory cytokine production, while stimulating anti-inflammatory cytokine secretion in ethanol or lipopolysaccharide-stimulated Kupffer cells/macrophages. It promotes M2-type macrophage polarization and metabolic reprogramming of glucose and lipid metabolism. PPC mitigates steatosis in NAFLD through inhibiting polarization of pro-inflammatory M1-type Kupffer cells, alleviating metabolic inflammation, remodeling hepatic lipid metabolism, correcting imbalances between lipogenesis and lipolysis and enhancing lipoprotein secretion from hepatocytes. PPC is antifibrotic by preventing progression of alcoholic hepatic fibrosis in baboons and also prevents CCl4-induced fibrosis in rats. PPC supplementation replenishes the phosphatidylcholine content of damaged cell membranes, resulting in increased membrane fluidity and functioning. Phosphatidylcholine repletion prevents increased membrane curvature of the endoplasmic reticulum and Golgi and decreases sterol regulatory element binding protein-1-mediated lipogenesis, reducing steatosis. PPC remodels gut microbiota and affects hepatic lipid metabolism via the gut-hepatic-axis and also alleviates brain inflammatory responses and cognitive impairment via the gut-brain-axis. Additionally, PPC protects extrahepatic tissues from injury caused by various toxic compounds by reducing oxidative stress, inflammation, and membrane damage. It also stimulates liver regeneration, enhances sensitivity of cancer cells to radiotherapy/chemotherapy, and inhibits experimental hepatocarcinogenesis. PPC's beneficial effects justify it as a supportive treatment of liver disease.

Tetrahydrocurcumin Add-On therapy to losartan in a rat model of diabetic nephropathy decreases blood pressure and markers of kidney injury

Tetrahydrocurcumin (THC), a principal metabolite of curcumin, was tested in a rat model of type 2 diabetes mellitus. THC was administered via daily oral gavage with the lipid carrier polyenylphosphatidylcholine (PPC) as add-on therapy to losartan (angiotensin receptor blocker) to examine effects on kidney oxidative stress and fibrosis. A combination of unilateral nephrectomy, high-fat diet and low-dose streptozotocin was used to induce diabetic nephropathy in male Sprague-Dawley rats. Animals with fasting blood glucose >200 mg/dL were randomized to PPC, losartan, THC + PPC or THC + PPC + losartan. Untreated chronic kidney disease (CKD) animals had proteinuria, decreased creatinine clearance, and evidence of kidney fibrosis on histology. THC + PPC + losartan treatment significantly lowered blood pressure concurrent with increased messenger RNA levels of antioxidant copper-zinc-superoxide dismutase and decreased protein kinase C-α, kidney injury molecule-1 and type I collagen in the kidneys; there was decreased albuminuria and a trend for increased creatinine clearance compared to untreated CKD rats. There was decreased fibrosis on kidney histology in PPC-only and THC-treated CKD rats. Plasma levels of kidney injury molecule-1 were decreased in THC + PPC + losartan animals. In summary, add-on THC to losartan therapy improved antioxidant levels and decreased fibrosis in the kidneys, and lowered blood pressure in diabetic CKD rats.

Beneficial Effects of Aerobic Exercise Training Combined with Rosiglitazone on Glucose Metabolism in Otsuka Long Evans Tokushima Fatty Rats

BACKGROUND

Regular aerobic exercise is essential for the prevention and management of type 2 diabetes mellitus and may be particularly beneficial for those treated with thiazolidinediones, since it may prevent associated weight gain. This study aimed to evaluate the effect of combined exercise and rosiglitazone treatment on body composition and glucose metabolism in obese diabetes-prone animals.

METHODS

We analyzed metabolic parameters, body composition, and islet profiles in Otsuka Long Evans Tokushima Fatty rats after 28 weeks of aerobic exercise, rosiglitazone treatment, and combined exercise and rosiglitazone treatment.

RESULTS

Combined exercise with rosiglitazone showed significantly less increase in weight and epididymal fat compared to rosiglitazone treatment. Aerobic exercise alone and combined rosiglitazone and exercise treatment led to similar retention of lean body mass. All experimental groups showed a decrease in fasting glucose. However, the combined exercise and rosiglitazone therapy group showed prominent improvement in glucose tolerance compared to the other groups. Rescue of islet destruction was observed in all experimental groups, but was most prominent in the combined therapy group.

CONCLUSION

Regular aerobic exercise combined with rosiglitazone treatment can compensate for the adverse effect of rosiglitazone treatment and has benefit for islet preservation.

Activity of essential phospholipids (EPL) from soybean in liver diseases

Essential phospholipids (EPL) contain a highly purified extract of polyenylphosphatidylcholine (PPC) molecules from soybean. The main active ingredient is 1,2-dilinoleoylphosphatidylcholine (DLPC), which differentiates it from other phospholipids, lecithins, or extracts from other sources. Although EPLis widely used in liver diseases of various origins, its mode of action and pharmacological and clinical evidence of its efficacy have not yet been concisely reviewed. This paper critically summarizes experimental and clinical results. With regard to in-vitro and animal tests, EPL influenced membrane-dependent cellular functions and showed anti-oxidant, anti-inflammatory, anti-fibrotic, apoptosis-modulating, regenerative, membrane-repairing and -protective, cell-signaling and receptor-influencing, as well as lipid-regulating effects in intoxication models with chemicals or drugs. Clinical studies, primarily from European and Asian countries, have shown improvement in subjective symptoms; clinical, biochemical and imaging findings; and histology in liver indications such as fatty liver of different origin, drug hepatotoxicity, and adjuvant in chronic viral hepatitis and hepatic coma. The available studies characterize EPL as evidence-based medicine, although further long-term controlled clinical trials are required to precisely determine its benefit for alleviating symptoms, improving well-being, inducing histological changes and slowing the progression of liver disease. EPL-related relevant side effects were not observed.

Histological and electron microscopic studies of the effect of beta-carotene on the pancreas of streptozotocin (STZ)-induced diabetic rats

To evaluate the protective effect of beta-carotene on induction of diabetes by streptozotocin (STZ), 45 albino rats, weighed about 110-130 g were used. They were divided randomly into six groups. GI rats used as control; GII rats were injected i.p. with a single dose of 40 mg streptozotocin (STZ) to become diabetic; GIII and GIV, the diabetic rats were injected i.p. with 0.3 and 0.1 mg beta-carotene, respectively; GV and GVI rats were injected i.p. only with 0.3 and 0.1 mg beta-carotene respectively. At the end of the experiment, the final body weights, blood glucose and insulin levels were determined and the values were statistically analyzed. Histological, semithin and ultrathin sections were prepared for pancreatic tissues. In the diabetic rats (GII), there was significant loss in body weight accompanied by significant increase in blood glucose levels. In addition, many light and electron microscopic changes were observed in the acinar and endocrine beta-cells of islets of pancreas. These changes were summarized as disturbance of acini arrangement, shrinkage and pyknotic nuclei, vacuolation and dissolution of mitochondria and Golgi elements, degranulation of beta-cells. In addition to the significant decrease in blood glucose levels, 0.3 mg beta-carotene (Gill) had decreased most of these changes than 0.1 mg of it (GIV). So, GIII provides more protection for the pancreatic tissue more than GIV. Also, the results revealed that injection of rats only with 0.3 and 0.1 mg beta-carotene (GV and GVI) had no observable changes in the pancreatic tissues, except that there was an increase in number of the vacuolized mitochondria in most acinar and beta-cells of islets. In conclusions, 0.3 mg beta-carotene could normalize the biochemical disorders of diabetes and provides more protection for the pancreatic tissues than 0.1 mg from the damaging effect of STZ to a greater extent.

Curcumin prevents streptozotocin-induced islet damage by scavenging free radicals: a prophylactic and protective role

Pancreatic islet cell death is the cause of deficient insulin production in diabetes mellitus. Approaches towards prevention of cell death are of prophylactic importance in control and management of hyperglycemia. Generation of oxidative stress is implicated in streptozotocin, a beta cell specific toxin-induced islet cell death. In this context, antioxidants raise an interest for therapeutic purposes. Curcumin, a common dietary spice is a well known antioxidant and hence we investigated its effect on streptozotocin-induced islet damage in vitro. Isolated islets from C57/BL6J mice were incubated with curcumin for 24 h and later exposed to streptozotocin for 8 h. The effect of streptozotocin exposure to islets was determined with respect to islet viability and functionality, cellular reactive oxygen species concentrations and levels of activated poly (ADP-ribose) polymerase-1. Cellular antioxidant potential (Cu/Zn superoxide dismutase) and advanced glycation end-product related damage was assessed to determine the metabolic status of treated and untreated islets. Islet viability and secreted insulin in curcumin pretreated islets were significantly higher than islets exposed to streptozotocin alone. Curcumin retarded generation of islet reactive oxygen species along with inhibition of Poly ADP-ribose polymerase-1 activation. Although curcumin did not cause overexpression of Cu/Zn superoxide dismutase, it prevented reduction in levels of cellular free radical scavenging enzymes. Our data shows that curcumin protects islets against streptozotocin-induced oxidative stress by scavenging free radicals. We show here for the first time, that prophylactic use of curcumin may effectively rescue islets from damage without affecting the normal function of these cellular structures.

Anti-diabetic Activity of SMK001, a Poly Herbal Formula in Streptozotocin Induced Diabetic Rats: Therapeutic Study

The therapeutic anti-diabetic effect of SMK001, a poly herbal formula was evaluated in the streptozotocin (STZ; 60 mg/kg, single intraperitoneal injection) induced diabetic rats. For therapeutic study, test articles were orally dosed once a day from 21 d after STZ-dosing at 100, 200 and 500 mg/kg/5 ml dosage levels for 4 weeks. The body weight changes, blood and urine glucose level changes were monitored with changes on the pancreas weight, and after sacrifice, the histopathological changes of pancreas and the changes of insulin- and glucagon-producing cells were also observed by immunohistochemistry. The results were compared to that of glibenclamide 5 mg/kg-dosing group. Significantly (p<0.01 or p<0.05) decrease of body weight, blood and urine glucose levels were detected in STZ-induced diabetic animals with disruption and disappearance of pancreatic islets. In addition, significantly (p<0.01) increase of glucagon- and decrease of insulin-producing cells were detected in STZ induced diabetic rats. However, these diabetic changes were significantly (p<0.01 or p<0.05) and dose dependently decreased in SMK001-dosing groups, and SMK001 100 mg/kg showed more favorable effects compared to that of glibenclamide 5 mg/kg. Based on these results, it is considered that SMK001 has favorable effect to inhibit the changes on the blood and urine glucose levels, body weight and the histopathological changes of pancreas in STZ induce diabetes.

Oral acute toxicity of polyenylphosphatidylcholine (PPC) in rats

Endogen phospholipids play a major role in determining the structure and nature of cell membranes. A deficiency of phospholipids in cellular membranes makes it almost impossible for the cell membrane to perform its function as a selective barrier between what passes in and out of the cell. Polyenylphosphatidylcholine chemical structure corresponds to that of endogen phospholipids, but it possesses functional superiority because of its content of unsaturated fatty acids. Polyenylphosphatidylcholine integrates in the cell membrane and organelle systems while becoming their constitutive elements. A healthy cell membrane leads to healthy cells and then healthy tissue and then to healthy organs or body systems and finally, healthy bodies and minds. For a long time, polyenylphosphatidylcholine in combination with vitamins has been used in the treatment of numerous health problems such as liver diseases, dyslipoproteinaemias and different intoxications with consequent liver failure. The main aim of toxicology studies is evaluation of the toxic potential and risks of human exposition to the substance. According to the Organization for Economic Cooperation and Development (OECD) acute oral toxicity refers to those adverse effects occurring following oral administration of a single dose of a substance or multiple doses given within 24 hours. LD50 (median lethal dose), oral, is a statistically derived single dose of a substance that can be expected to cause death in 50 per cent of animals when administered by the oral route. Our acute toxicity study was performed on albino Wistar rats. Animals were randomised in three experimental and one control group, each of 5 males and 5 females. Study was based on the administration of a single oral dose of the test substance (polyenylphosphatidylcholine) to each experimental animal. There were three dose-levels of the test substance: 300, 500 and 1000 mg/kg. Test substance administration day was the first day of the observation period that lasted 14 days. Control animals were given milk vehicle. At the end of the study, no statistically significant differences between experimental and control animals were observed concerning the recorded parameters: body weight, respiratory rate, tremor, faeces and phonation quality, indicating the absence of the test substance acute toxicity.

Application of ion etching to immunoscanning electron microscopy

A method for achieving both the light and electron microscopic observations of the same immunolabeled semithin section is described. Mild ion etching (IE) was performed on the semithin LR white resin sections of rat pancreas to evaluate conditions for scanning electron microscopic secondary electron image observations. Before immunocytochemical staining, very mild, rapid etching was conducted as follows: ionization voltage 300 V, operating vacuum 35 Pa, and etching time 1 min, employing an ion coater above sections on glass slides. The sections were immunohistochemically stained with anti-insulin and immunogold in association with silver enhancement techniques for light microscopic observation, in which B cells in pancreatic islets were positively stained brown. Subsequently, essential mild IE was performed over the stained section as follows: 350 V, 38 Pa, 29 min. The samples were coated with platinum for scanning electron microscopic secondary electron images, in which the cores of secretory granules of the B cells were positively labeled with gold-silver particles. The present method is suitable for detection of substances involving immunogold labeling. It enables us to obtain high-resolution images at low magnification that can be correlated with light microscopic observations. Middle to high magnifications are applicable for detailed observations with secondary electron imaging scanning electron microscopy.

Leucine culture reveals that ATP synthase functions as a fuel sensor in pancreatic beta-cells

Our goal was to investigate whether leucine culture affects beta-cell glucose sensing. One-day culture of rat islets with 10 mM leucine had no effect on glucose-induced insulin secretion. One-week leucine culture decreased the threshold for glucose-induced insulin secretion and increased maximal insulin secretion at 30 mM glucose. Glucose-induced cytosolic free Ca(2+) was increased at 1 week but not at 1 day of leucine culture. Without glucose, ATP content was not different with or without leucine culture for 1 week. With 20 mM glucose, ATP content was higher by 1.5-fold in islets cultured for 1 week with leucine than those without leucine. Microarray experiments indicated that culture of RINm5F cells with leucine increased expression of ATP synthase beta subunit 3.2-fold, which was confirmed by real time reverse transcription-PCR analysis (3.0- +/- 0.4-fold) in rat islets at 1 week but not after 1 day with leucine culture. Down-regulation of ATP synthase beta subunit by siRNA decreased INS1 cell ATP content and insulin secretion with 20 mM glucose. Overexpression of ATP synthase beta subunit in INS1 cell increased insulin secretion in the presence of 5 and 20 mM glucose. In conclusion, one-week leucine culture of rat islets up-regulated ATP synthase and increased ATP content, which resulted in elevated [Ca(2+)] levels and more insulin exocytosis by glucose. Depletion of ATP synthase beta subunit with siRNA produced opposite effects. These data reveal the fuel-sensing role of mitochondrial ATP synthase in the control of ATP production from glucose and the control of glucose-induced insulin secretion.