Increased fat absorption and impaired fat clearance cause postprandial hypertriglyceridemia in Spontaneously Diabetic Torii rat

The dichloromethane fraction from Calotropis gigantea (L.) dryand. Stem bark extract prevents liver cancer in SDT rats with insulin-independent diabetes mellitus

ETHNOPHARMACOLOGICAL RELEVANCE

Calotropis gigantea (L.) Dryand. (C. gigantea) is a traditional medicinal plant, recognized for its effectiveness in managing diabetes, along with its notable antioxidant, anti-inflammatory, and anticancer properties. Type II diabetes mellitus (T2DM) is characterized by chronic metabolic disorders associated with an elevated risk of hepatocellular carcinoma (HCC) due to hyperglycemia and impaired insulin response. The scientific validation of C. gigantea's ethnopharmacological efficacy offers advantages in alleviating cancer progression in T2DM complications, enriching existing knowledge and potentially aiding future clinical cancer treatments.

AIM

This study aimed to investigate the preventive potential of the dichloromethane fraction of C. gigantea stem bark extract (CGDCM) against diethylnitrosamine (DEN)-induced HCC in T2DM rats, aiming to reduce cancer incidence associated with diabetes while validating C. gigantea's ethnopharmacological efficacy.

MATERIALS AND METHODS

Spontaneously Diabetic Torii (SDT) rats were administered DEN to induce HCC (SDT-DEN-VEH), followed by treatment with CGDCM. Metformin was used as a positive control (SDT-DEN-MET). All the treatments were administered for 10 weeks after the initial DEN injection. Diabetes-related parameters, including serum levels of glucose, insulin, and glycosylated hemoglobin (HbA1c), as well as liver function enzymes (aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and gamma-glutamyl transferase), were quantified. Serum inflammation biomarkers interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were evaluated. Liver tissue samples were analyzed for inflammation protein expression (IL-6, TNF-α, transforming growth factor-β1 (TGF-β1), and α-smooth muscle actin (α-SMA)). Histopathological evaluation was performed to assess hepatic necrosis, inflammation, and fibrosis. Liver cell proliferation was determined using immunohistochemistry for Ki-67 expression.

RESULTS

Rats with SDT-DEN-induced HCC treated with CGDCM exhibited reduced serum glucose levels, elevated insulin levels, and decreased HbA1c levels. CGDCM treatment also reduced elevated hepatic IL-6, TNF-α, TGF-β1, and α-SMA levels in SDT-DEN-VEH rats. Additionally, CGDCM treatment prevented hepatocyte damage, fibrosis, and cell proliferation. No adverse effects on normal organs were observed with CGDCM treatment, suggesting its safety for the treatment of HCC complications associated with diabetes. Additionally, the absence of adverse effects in SD rats treated with CGDCM at 2.5 mg/kg further supports the notion of its safe usage.

CONCLUSIONS

These findings suggest that C. gigantea stem bark extract exerts preventive effects against the development of HCC complications in patients with T2DM, expanding the potential benefits of its ethnopharmacological advantages.

Intestinal lipid absorption and transport in type 2 diabetes

Postprandial hyperlipidaemia is an important feature of diabetic dyslipidaemia and plays an important role in the development of cardiovascular disease in individuals with type 2 diabetes. Postprandial hyperlipidaemia in type 2 diabetes is secondary to increased chylomicron production by the enterocytes and delayed catabolism of chylomicrons and chylomicron remnants. Insulin and some intestinal hormones (e.g. glucagon-like peptide-1 [GLP-1]) influence intestinal lipid metabolism. In individuals with type 2 diabetes, insulin resistance and possibly reduced GLP-1 secretion are involved in the pathophysiology of postprandial hyperlipidaemia. Several factors are involved in the overproduction of chylomicrons: (1) increased expression of microsomal triglyceride transfer protein, which is a key enzyme in chylomicron synthesis; (2) higher stability and availability of apolipoprotein B-48; and (3) increased de novo lipogenesis. Individuals with type 2 diabetes present with disorders of cholesterol metabolism in the enterocytes with reduced absorption and increased synthesis. The increased production of chylomicrons in type 2 diabetes is also associated with a reduction in their catabolism, mostly because of a reduction in activity of lipoprotein lipase. Modification of the microbiota, which is observed in type 2 diabetes, may also generate disorders of intestinal lipid metabolism, but human data remain limited. Some glucose-lowering treatments significantly influence intestinal lipid absorption and transport. Postprandial hyperlipidaemia is reduced by metformin, pioglitazone, alpha-glucosidase inhibitors, dipeptidyl peptidase 4 inhibitors and GLP-1 agonists. The most pronounced effect is observed with GLP-1 agonists, which reduce chylomicron production significantly in individuals with type 2 diabetes and have a direct effect on the intestine by reducing the expression of genes involved in intestinal lipoprotein metabolism. The effect of sodium-glucose cotransporter 2 inhibitors on intestinal lipid metabolism needs to be clarified.

Olive oil consumption and its repercussions on lipid metabolism

Consumption of highly processed foods, such as those high in trans fats and free sugars, coupled with sedentarism and chronic stress increases the risk of obesity and cardiometabolic disorders, while adherence to a Mediterranean diet is inversely associated with the prevalence of such diseases. Olive oil is the main source of fat in the Mediterranean diet. Data accumulated thus far show consumption of extra virgin, (poly)phenol-rich olive oil to be associated with specific health benefits. Of note, recommendations for consumption based on health claims refer to the phenolic content of extra virgin olive oil as beneficial. However, even though foods rich in monounsaturated fatty acids, such as olive oil, are healthier than foods rich in saturated and trans fats, their inordinate use can lead to adverse effects on health. The aim of this review was to summarize the data on olive oil consumption worldwide and to critically examine the literature on the potential adverse effects of olive oil and its main components, particularly any effects on lipid metabolism. As demonstrated by substantial evidence, extra virgin olive oil is healthful and should be preferentially used within the context of a balanced diet, but excessive consumption may lead to adverse consequences.

Postprandial dyslipidemia in insulin resistant states in adolescent populations

Obesity and the metabolic syndrome are becoming increasingly prevalent not only in adults, but also in adolescents. The metabolic syndrome, a complex cluster of metabolic abnormalities, increases one's risk of developing type 2 diabetes and cardiovascular disease (CVD). Dyslipidemia, a key component of the metabolic syndrome, is highly associated with insulin resistance and contributes to increased CVD risk. Dyslipidemia has traditionally been assessed using a fasting lipid profile [i.e. fasting triglycerides, total cholesterol, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C)]. However, the postprandial state predominates over the course of a day and non-fasting triglycerides independently predict CVD risk. In insulin resistant states, the intestine overproduces triglyceride-rich lipoprotein (TRL) particles, termed chylomicrons (CMs), following ingestion of a fat-containing meal, as well as in the fasting state. Along with elevated hepatic TRLs (i.e. very-low density lipoproteins), CMs contribute to remnant lipoprotein accumulation, small dense LDL particles, and reduced HDL-C, which collectively increase CVD risk. Given the early genesis of atherosclerosis and physiological metabolic changes during adolescence, studying postprandial dyslipidemia in the adolescent population is an important area of study. Postprandial dyslipidemia in the pediatric population poses a significant public health concern, warranting a better understanding of its pathogenesis and association with insulin resistance and CVD. This review discusses the metabolic syndrome, focusing on the link between insulin resistance, postprandial dyslipidemia, and CVD risk. Furthermore, the clinical significance and functional assessment of postprandial dyslipidemia, specifically in the adolescent population, is discussed in more detail.

Rice bran oil and canola oil improve blood lipids compared to sunflower oil in women with type 2 diabetes: A randomized, single-blind, controlled trial

BACKGROUND

Hypolipidemic effects of vegetable oils have been demonstrated in a number of studies, but there is no study, which compares the effects of canola oil (CO) and rice bran oil (RBO) on diabetic patient. We aimed to compare the effects of CO and RBO consumption on blood lipids in women with type 2 diabetes.

METHODS

Seventy-five postmenopausal women with type 2 diabetes participated in this single-center, randomized, controlled, parallel-group trial in Shiraz, Iran. Participants were randomly allocated to three groups including a control group (balance diet + 30 g/d sunflower oil) and two intervention groups (balance diet + 30 g/day CO or RBO). At baseline and after 8 weeks, serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) were measured.

RESULTS

At 8 weeks, mean of serum levels of TG (mg/dL), TC (mg/dL), and LDL-C (mg/dL) significantly decreased in the CO group (-23.66, P < .001; -11.92, P < .001; and -6.33, P = .013, respectively) and RBO group (-38.62, P < .001; -17.25, P < .001; and -8.90, P = .002, respectively) compared with the controls (7.01, 4.06, and 2.90, respectively). Also, in comparison with CO group, the changes of TG, LDL-C, and non-HDL-C levels were significantly more in the RBO group (P = .007, P = .012, and P = .011, respectively). Levels of serum HDL-C remained unchanged in all groups at the end of study.

CONCLUSIONS

Substitution of RBO or CO for sunflower oil could attenuate lipid disorders in type 2 diabetes women. Moreover, RBO could improve lipid profile more efficiently than CO.

Identification of a botanical inhibitor of intestinal diacylglyceride acyltransferase 1 activity via in vitro screening and a parallel, randomized, blinded, placebo-controlled clinical trial

Background

Diacylglyceride acyltransferase 1 (DGAT1) is the enzyme that adds the final fatty acid on to a diacylglyceride during triglyceride (TG) synthesis. DGAT1 plays a key role in the repackaging of dietary TG into circulating TG rich chylomicrons. A growing amount of research has indicated that an exaggerated postprandial circulating TG level is a risk indicator for cardiovascular and metabolic disorders. The aim of this research was to identify a botanical extract that inhibits intestinal DGAT1 activity and attenuates postprandial hypertriglyceridemia in overweight and obese humans.

Methods

Twenty individual phytochemicals and an internal proprietary botanical extract library were screened with a primary cell-free DGAT1 enzyme assay that contained dioleoyl glycerol and palmitoleoyl Coenzyme A as substrates plus human intestinal microsomes as the DGAT1 enzyme source. Botanical extracts with IC50 values < 100 μg/mL were evaluated in a cellular DGAT1 assay. The cellular DGAT1 assay comprised the analysis of ¹⁴C labeled TG synthesis in cells incubated with ¹⁴C-glycerol and 0.3 mM oleic acid. Lead botanical extracts were then evaluated in a parallel, double-blind, placebo-controlled clinical trial. Ninety healthy, overweight and obese participants were randomized to receive 2 g daily of placebo or individual botanical extracts (the investigational product) for seven days. Serum TG levels were measured before and after consuming a high fat meal (HFM) challenge (0.354 L drink/shake; 77 g fat, 25 g carbohydrate and 9 g protein) as a marker of intestinal DGAT1 enzyme activity.

Results

Phenolic acids (i.e., gallic acid) and polyphenols (i.e., cyanidin) abundantly found in nature appeared to inhibit DGAT1 enzyme activity in vitro. Four polyphenolic rich botanical extracts were identified from in vitro evaluation in both cell-free and cellular model systems: apple peel extract (APE), grape extract (GE), red raspberry leaf extract (RLE) and apricot/nectarine extract (ANE) (IC50 = 1.4, 5.6, and 10.4 and 3.4 μg/mL, respectively). In the seven day clinical trial, compared to placebo, only GE significantly reduced the baseline subtracted change in serum TG AUC following consumption of the HFM (AUC = 281 ± 37 vs. 181 ± 30 mg/dL*h, respectively; P = 0.021). Chromatographic characterization of the GE revealed a large number of closely eluting components containing proanthocyanidins, catechins, anthocyanins and their secondary metabolites that corresponded with the observed DGAT1 enzyme inhibition in the cell-free model.

Conclusion

These data suggest that a dietary GE has the potential to attenuate postprandial hypertriglyceridemia in part by the inhibition of intestinal DGAT1 enzyme activity without intolerable side effects.

Trial registration

This trial was registered with ClinicalTrials.gov NCT02333461

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-015-0025-2) contains supplementary material, which is available to authorized users.

Key intestinal genes involved in lipoprotein metabolism are downregulated in dyslipidemic men with insulin resistance

Insulin resistance (IR) is associated with elevated plasma levels of triglyceride-rich lipoproteins (TRLs) of intestinal origin. However, the mechanisms underlying the overaccumulation of apolipoprotein (apo)B-48-containing TRLs in individuals with IR are not yet fully understood. This study examined the relationships between apoB-48-containing TRL kinetics and the expression of key intestinal genes and proteins involved in lipid/lipoprotein metabolism in 14 obese nondiabetic men with IR compared with 10 insulin-sensitive (IS) men matched for waist circumference. The in vivo kinetics of TRL apoB-48 were assessed using a primed-constant infusion of L-[5,5,5-D₃]leucine for 12 h with the participants in a constantly fed state. The expression of key intestinal genes and proteins involved in lipid/lipoprotein metabolism was assessed by performing real-time PCR quantification and LC-MS/MS on duodenal biopsy specimens. The TRL apoB-48 pool size and production rate were 102% (P < 0.0001) and 87% (P = 0.01) greater, respectively, in the men with IR versus the IS men. On the other hand, intestinal mRNA levels of sterol regulatory element binding factor-2, hepatocyte nuclear factor-4α, and microsomal triglyceride transfer protein were significantly lower in the men with IR than in the IS men. These data indicate that IR is associated with intestinal overproduction of lipoproteins and significant downregulation of key intestinal genes involved in lipid/lipoprotein metabolism.

The spontaneously diabetic torii rat: an animal model of nonobese type 2 diabetes with severe diabetic complications

The Spontaneously Diabetic Torii (SDT) rat is an inbred strain of Sprague-Dawley rat and recently is established as a nonobese model of type 2 diabetes (T2D). Male SDT rats show high plasma glucose levels (over 700 mg/dL) by 20 weeks. Male SDT rats show pancreatic islet histopathology, including hemorrhage in pancreatic islets and inflammatory cell infiltration with fibroblasts. Prior to the onset of diabetes, glucose intolerance with hypoinsulinemia is also observed. As a result of chronic severe hyperglycemia, the SDT rats develop profound complications. In eyes, retinopathy, cataract, and neovascular glaucoma are observed. Proliferative retinopathy, especially, resulting from retinal neovascular vessels is a unique characteristic of this model. In kidney, mesangial proliferation and nodular lesion are observed. Both peripheral neuropathy such as decreased nerve conduction velocity and thermal hypoalgesia and autonomic neuropathy such as diabetic diarrhea and voiding dysfunction have been reported. Osteoporosis is another complication characterized in SDT rat. Decreased bone density and low-turnover bone lesions are observed. Taking advantage of these features, SDT rat has been used for evaluating antidiabetic drugs and drugs/gene therapy for diabetic complications. In conclusion, the SDT rat is potentially a useful T2D model for studies on pathogenesis and treatment of diabetic complications in humans.

Gut triglyceride production

Our knowledge of how the body absorbs triacylglycerols (TAG) from the diet and how this process is regulated has increased at a rapid rate in recent years. Dietary TAG are hydrolyzed in the intestinal lumen to free fatty acids (FFA) and monoacylglycerols (MAG), which are taken up by enterocytes from their apical side, transported to the endoplasmic reticulum (ER) and resynthesized into TAG. TAG are assembled into chylomicrons (CM) in the ER, transported to the Golgi via pre-chylomicron transport vesicles and secreted towards the basolateral side. In this review, we mainly focus on the roles of key proteins involved in uptake and intracellular transport of fatty acids, their conversion to TAG and packaging into CM. We will also discuss intracellular transport and secretion of CM. Moreover, we will bring to light few factors that regulate gut triglyceride production. Furthermore, we briefly summarize pathways involved in cholesterol absorption. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

Acute hypertriglyceridemia promotes intestinal lymphatic lipid and drug transport: a positive feedback mechanism in lipid and drug absorption

Elevated systemic levels of triglyceride-rich lipoproteins (TRL) are a risk factor for the development of atherosclerosis. In patients with metabolic syndrome (MetS), intestinal TRL overproduction contributes to high systemic TRL levels, and recent studies suggest that systemic changes in MetS such as increases in plasma fatty acids and insulin resistance stimulate intestinal TRL production. The current study has examined whether increases in systemic TRL influence intestinal lipid transport and lipoprotein assembly pathways and evaluates the impact of these changes on the absorption and lymphatic transport of lipids and a model lipophilic drug (halofantrine). Mesenteric lymph-duct or bile-duct cannulated rats were administered IV saline or (14)C-labeled chylomicron (CM) (to increase systemic TRL) and intraduodenal (3)H lipids and drug. Changes to biliary lipid output and lymphatic lipid and drug transport were subsequently examined. Increasing systemic TRL concentrations stimulated a significant increase in lymphatic lipid and drug transport. The increased lipids in lymph were not derived from bile or the intestinal blood supply (fatty acid or IV infused (14)C-CM). Rather, an increase in lymphatic transport of duodenally sourced lipids was evident. Increasing plasma levels of TRL therefore stimulated lipid absorption and lymphatic transport via a positive feedback process. The data also suggest that the changes to intestinal TRL formation that result from raised systemic TRL levels may impact on the absorption of highly lipophilic drugs and therefore the reproducibility of drug treatments.

Pharmacological characterization of diethyl-2-({3-dimethylcarbamoyl-4-[(4'-trifluoromethylbiphenyl-2-carbonyl)amino]phenyl}acetyloxymethyl)-2-phenylmalonate (JTT-130), an intestine-specific inhibitor of microsomal triglyceride transfer protein

Inhibitors of microsomal triglyceride transfer protein (MTP) expressed in the liver and small intestine are potential candidates for lipid-lowering agents. However, inhibition of hepatic MTP could lead to significant safety issues such as fatty liver disease. To develop a specific inhibitor of intestinal MTP, JTT-130 [diethyl-2-({3-dimethylcarbamoyl-4-[(4'-trifluoromethylbiphenyl-2-carbonyl)amino]phenyl}acetyloxymethyl)-2-phenylmalonate], was designed to be rapidly hydrolyzed in the absorption process. Here, we describe JTT-130, an intestine-specific MTP inhibitor, and evaluate its pharmacological properties. In in vitro metabolic stability tests, JTT-130 was readily hydrolyzed during incubation with liver S9 from humans, hamsters, and rats. In an in vitro triglyceride (TG) transfer assay with human intestinal MTP, JTT-130 potently inhibited TG transfer activity with an IC(50) value of 0.83 nM. When orally administered to hamsters, JTT-130 significantly suppressed an increase in chylomicron-TG after olive oil loading at 0.3 mg/kg and above but did not inhibit TG secretion from the liver at doses of up to 1000 mg/kg, indicating an inhibitory action highly specific for the small intestine. In rats orally administered [(14)C]triolein, JTT-130 potently suppressed an increase in blood (14)C radioactivity and increased (14)C radioactivity in the upper small intestine and the intestinal lumen. In hyperlipidemic hamsters fed a high-fat and high-cholesterol diet, repeated dosing with JTT-130 for 2 weeks reduced TG and cholesterol levels in the plasma and TG content in the liver. These results indicated that JTT-130 is a potent inhibitor specific to intestinal MTP and suggested that JTT-130 would be a useful compound for the treatment of dyslipidemia without inducing hepatotoxicity.

Pathophysiological characteristics of diabetic ocular complications in spontaneously diabetic torii rat

The Spontaneously Diabetic Torii (SDT) rat, a nonobese type 2 diabetes model, develops severe diabetic retinopathy as result of chronic severe hyperglycemia. Although existing diabetes animal models also develop ocular complications, severe retinal lesions frequently observed in human diabetes patients such as preretinal neovascularization or retinal detachment are not found. Distinctive features in SDT rat are hypermature cataract, tractional retinal detachment with fibrous proliferation, and massive hemorrhaging in the anterior chamber. These pathophysiological changes are caused by sustained hyperglycemic condition and subsequent increased expression of vascular endothelial growth factor (VEGF) in retina, iris, and ciliary body. Although some differences in diabetic retinopathy exist between SDT rats and humans (e.g., a low incidence of neovascular formation and poor development of nonperfused area are found in this animal), SDT rat will be a useful model in studies of the pathogenesis and treatment of diabetic retinopathy.

Nutrient-driven incretin secretion into intestinal lymph is different between diabetic Goto-Kakizaki rats and Wistar rats

The incretin hormones gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) augment postprandial glucose-mediated insulin release from pancreatic beta-cells. The Goto-Kakizaki (GK) rat is a widely used, lean rodent model of Type 2 diabetes; however, little is known regarding the incretin secretion profile to different nutrients in these rats. We have recently shown that lymph is a sensitive medium to measure incretin secretion in rodents and probably the preferred compartment for GLP-1 monitoring. To characterize the meal-induced incretin profile, we compared lymphatic incretin concentrations in the GK and Wistar rat after enteral macronutrient administration. After cannulation of the major mesenteric lymphatic duct and duodenum, each animal received an intraduodenal bolus of either a fat emulsion, dextrin, a mixed meal, or saline. Lymph was collected for 3 h and analyzed for triglyceride, glucose, GLP-1, and GIP content. There was no statistical difference in GIP or GLP-1 secretion after a lipid bolus between GK and Wistar rats. Dextrin and a mixed meal both increased incretin concentration area under the curve, however, significantly less in GK rats compared with Wistar rats (dextrin GIP: 707 +/- 106 vs. 1,373 +/- 114 pg ml(-1) h, respectively, P < 0.001; dextrin GLP-1: 82.7 +/- 24.3 vs. 208.3 +/- 26.3 pM/h, respectively, P = 0.001). After administration of a carbohydrate-containing meal, GK rats were unable to mount as robust a response of both GIP and GLP-1 compared with Wistar rats, a phenomenon not seen after a lipid meal. We propose a similar, glucose-mediated incretin secretion pathway defect of both K and L cells in GK rats.

Intestinal lipoprotein overproduction in insulin-resistant states

PURPOSE OF REVIEW

Excessive postprandial lipemia is highly prevalent in obese and insulin-resistant/type 2 diabetic individuals and substantially increases the risk of atherosclerosis and cardiovascular disease. This article will review our current understanding of the link between insulin resistance and intestinal lipoprotein overproduction and highlight some of the key recent findings in the field.

RECENT FINDINGS

Emerging evidence from several animal models of insulin resistance as well as insulin-resistant humans clearly supports the link between insulin resistance and aberrant intestinal lipoprotein metabolism. In insulin-resistant states, elevated free fatty acid flux into the intestine, downregulation of intestinal insulin signaling and upregulation of microsomal triglyceride transfer protein all appear to stimulate intestinal lipoprotein production. Gut peptides, GLP-1 and GLP-2, may be important regulators of intestinal lipid absorption and lipoprotein production.

SUMMARY

Available evidence in humans and animal models strongly favors the concept that the small intestine is not merely an absorptive organ but rather plays an active role in regulating the rate of production of triglyceride-rich lipoproteins. Metabolic signals in insulin resistance and type 2 diabetes and in some cases an aberrant intestinal response to these factors all contribute to the enhanced formation and secretion of triglyceride-rich lipoproteins.