Endogenous and diet-induced hypercholesterolemia in nonhuman primates: effects of age, adiposity, and diabetes on lipoprotein profiles

A virus-like particle-based bivalent PCSK9 vaccine lowers LDL-cholesterol levels in non-human primates

Elevated low-density lipoprotein cholesterol (LDL-C) is an important risk factor in the development of atherosclerotic cardiovascular disease (ASCVD). Inhibitors of proprotein convertase subtilisin/kexin type 9 (PCSK9), a negative regulator of LDL-C metabolism, have emerged as promising approaches for reducing elevated LDL-C levels. Here, we evaluated the cholesterol-lowering efficacy of virus-like particle (VLP) based vaccines that target epitopes found within the LDL receptor (LDL-R) binding domain of PCSK9. In both mice and non-human primates, a bivalent VLP vaccine targeting two distinct epitopes on PCSK9 elicited strong and durable antibody responses and lowered cholesterol levels. In macaques, a VLP vaccine targeting a single PCSK9 epitope was only effective at lowering LDL-C levels in combination with statins, whereas immunization with the bivalent vaccine lowered LDL-C without requiring statin co-administration. These data highlight the efficacy of an alternative, vaccine-based approach for lowering LDL-C.

A Virus-like particle-based bivalent PCSK9 vaccine lowers LDL-cholesterol levels in Non-Human Primates

Elevated low-density lipoprotein cholesterol (LDL-C) is an important risk factor in the development of atherosclerotic cardiovascular disease (ASCVD). Inhibitors of proprotein convertase subtilisin/kexin type 9 (PCSK9), a negative regulator of LDL-C metabolism, have emerged as promising approaches for reducing elevated LDL-C levels. Here, we evaluated the cholesterol lowering efficacy of virus-like particle (VLP) based vaccines that target epitopes found within the LDL receptor (LDL-R) binding domain of PCSK9. In both mice and non-human primates, a bivalent VLP vaccine targeting two distinct epitopes on PCSK9 elicited strong and durable antibody responses and lowered cholesterol levels. In macaques, a VLP vaccine targeting a single PCSK9 epitope was only effective at lowering LDL-C levels in combination with statins, whereas immunization with the bivalent vaccine lowered LDL-C without requiring statin co-administration. These data highlight the efficacy of an alternative, vaccine-based approach for lowering LDL-C.

Use and Importance of Nonhuman Primates in Metabolic Disease Research: Current State of the Field

Obesity and its multiple metabolic sequelae, including type 2 diabetes, cardiovascular disease, and fatty liver disease, are becoming increasingly widespread in both the developed and developing world. There is an urgent need to identify new approaches for the prevention and treatment of these costly and prevalent metabolic conditions. Accomplishing this will require the use of appropriate animal models for preclinical and translational investigations in metabolic disease research. Although studies in rodent models are often useful for target/pathway identification and testing hypotheses, there are important differences in metabolic physiology between rodents and primates, and experimental findings in rodent models have often failed to be successfully translated into new, clinically useful therapeutic modalities in humans. Nonhuman primates represent a valuable and physiologically relevant model that serve as a critical translational bridge between basic studies performed in rodent models and clinical studies in humans. The purpose of this review is to evaluate the evidence, including a number of specific examples, in support of the use of nonhuman primate models in metabolic disease research, as well as some of the disadvantages and limitations involved in the use of nonhuman primates. The evidence taken as a whole indicates that nonhuman primates are and will remain an indispensable resource for evaluating the efficacy and safety of novel therapeutic strategies targeting clinically important metabolic diseases, including dyslipidemia and atherosclerosis, type 2 diabetes, hepatic steatosis, steatohepatitis, and hepatic fibrosis, and potentially the cognitive decline and dementia associated with metabolic dysfunction, prior to taking these therapies into clinical trials in humans.

Transplantation of bone marrow mesenchymal stem cells for the treatment of type 2 diabetes in a macaque model

Bone marrow mesenchymal stem cells (BMSCs) are self-renewing, multipotent cells that can migrate to pathological sites and thereby provide a new treatment in diabetic animals. Superparamagnetic iron oxide/4',6-diamidino-2-phenylindole (DAPI) double-labeled BMSCs were transplanted into the pancreatic artery of macaques to treat type 2 diabetes mellitus (T2DM). The treatment efficiency of BMSCs was also evaluated. After successful induction of the T2DM model, the treatment group received double-labeled BMSCs via the pancreatic artery. Six weeks after BMSC transplantation, the fasting blood glucose and blood lipid levels measured in the treatment group were significantly lower (p < 0.05) than in the model group, although they were not reduced to normal levels (p < 0.05). Additionally, the serum C-peptide levels were significantly increased (p < 0.05). An intravenous glucose tolerance test and C-peptide release test had significant changes to the area under the curve. Within 14 days of the transplantation of labeled cells, the pancreatic and kidney tissue of the treatment group emitted a negative signal that was visible on magnetic resonance imaging (MRI). Six weeks after transplantation, DAPI signals appeared in the pancreatic and kidney tissue, which indicates that the BMSCs were mainly distributed in damaged tissue. Labeled stem cells can be used to track migration and distribution in vivo by MRI. In conclusion, the transplantation of BMSCs for the treatment of T2DM is safe and effective.

Effects of short-term niacin treatment on plasma lipoprotein concentrations in African green monkeys (Chlorocebus aethiops)

Niacin is the most effective drug available for raising levels of high-density lipoprotein (HDL) cholesterol. To evaluate its effects on plasma lipid concentrations, the authors administered a low dose of niacin to healthy, adult, female African green monkeys for 3 months. In the treated monkeys, low-density lipoprotein cholesterol concentrations decreased by 43% from baseline, whereas concentrations of HDL cholesterol and apolipoprotein A-I increased by 49% and 34%, respectively. The results suggest that in this primate model, a low dose of niacin can effectively increase concentrations of HDL cholesterol.

A preliminary report on oral fat tolerance test in rhesus monkeys

Background

Oral fat tolerance test (OFTT) has been widely used to assess the postprandial lipemia in human beings, but there is few studies concerning OFTT in nonhuman primates. This study is designed to explore the feasibility of OFTT in rhesus monkeys.

Methods

In a cross-over study, a total of 8 adult female rhesus monkeys were fed with normal monkey diet (NND), high sugar high fat diet (HHD), and extremely high fat diet (EHD), respectively. Each monkey consumed NND, HHD and EHD respectively, each weighing 60 g. Serial blood samples were collected at 1, 2, 3, 4, 5, and 6 h after ingesting each kind of food. Triglyceride, cholesterol, glucose, and insulin at each time point were measured. The area under the curve of triglyceride (TG-AUC) and triglyceride peak response (TG-PR) were also calculated.

Results

All monkeys ingested 3 kinds of foods within 15 minutes. TG-AUC and TG-PR of HHD group were higher than those of the other two groups. Postprandial triglyceride levels at 2, 3, 4, and 5 hours in HHD group during OFTT were also higher than those in NND and EHD group.

Conclusions

HHD diet can be used in OFTT for nonhuman primates.

Sex-specific heritability of spontaneous lipid levels in an extended pedigree of Indian-origin rhesus macaques (Macaca mulatta)

The rhesus macaque is an important model for human atherosclerosis but genetic determinants of relevant phenotypes have not yet been investigated in this species. Because lipid levels are well-established and heritable risk factors for human atherosclerosis, our goal was to assess the heritability of lipoprotein cholesterol and triglyceride levels in a single, extended pedigree of 1,289 Indian-origin rhesus macaques. Additionally, because increasing evidence supports sex differences in the genetic architecture of lipid levels and lipid metabolism in humans and macaques, we also explored sex-specific heritability for all lipid measures investigated in this study. Using standard methods, we measured lipoprotein cholesterol and triglyceride levels from fasted plasma in a sample of 193 pedigreed rhesus macaques selected for membership in large, paternal half-sib cohorts, and maintained on a low-fat, low cholesterol chow diet. Employing a variance components approach, we found moderate heritability for total cholesterol (h²=0.257, P=0.032), LDL cholesterol (h²=0.252, P=0.030), and triglyceride levels (h²=0.197, P=0.034) in the full sample. However, stratification by sex (N=68 males, N=125 females) revealed substantial sex-specific heritability for total cholesterol (0.644, P=0.004, females only), HDL cholesterol (0.843, P=0.0008, females only), VLDL cholesterol (0.482, P=0.018, males only), and triglyceride levels (0.705, P=0.001, males only) that was obscured or absent when sexes were combined in the full sample. We conclude that genes contribute to spontaneous variation in circulating lipid levels in the Indian-origin rhesus macaque in a sex-specific manner, and that the rhesus macaque is likely to be a valuable model for sex-specific genetic effects on lipid risk factors for human atherosclerosis. These findings are a first-ever report of heritability for cholesterol levels in this species, and support the need for expanded analysis of these traits in this population.

Serum metabolic variables associated with impaired glucose tolerance induced by high-fat-high-cholesterol diet in Macaca mulatta

Dyslipidemia caused by 'Western-diet pattern' is a strong risk factor for the onset of diabetes. This study aimed to disclose the relationship between the serum metabolite changes induced by habitual intake of high-fat and high-cholesterol (HFHC) diet and the development of impaired glucose tolerance (IGT) and insulin resistance through animal models of Macaca mulatta. Sixteen M. mulatta (six months old) were fed a control diet or a HFHC diet for 18 months. The diet effect on serum metabolic profiles was investigated by longitudinal research. Islet function was assessed by intravenous glucose tolerance and hyperinsulinemic-euglycemic clamp test. Metabonomics were determined by (1)H proton nuclear magnetic resonance spectroscopy. Prolonged diet-dependent hyperlipidemia facilitated visceral fat accumulation in liver and skeletal muscle and disorder of glucose homeostasis in juvenile monkeys. Glucose disappearance rate (K(Glu)) and insulin response to the glucose challenge effects in HFHC monkeys were significantly lower than in control monkeys. Otherwise, serum trimethylamine-N-oxide (TMAO), lactate and leucine/isoleucine were significantly higher in HFHC monkeys. Sphingomyelin and choline were the most positively correlated with K(Glu) (R(2) = 0.778), as well as negative correlation (R(2) = 0.64) with total cholesterol. The HFHC diet induced visceral fat, abnormal lipid metabolism and IGT prior to weight gain and body fat content increase in juvenile monkeys. We suggest that increased serum metabolites, such as TMAO, lactate, branched-chain amino acids and decreased sphingomyelin and choline, may serve as possible predictors for the evaluation of IGT and insulin resistance risks in the prediabetic state.

Investigation and treatment of type 2 diabetes in nonhuman primates

Nonhuman primates provide the ideal animal model for discovering and examining further the mechanisms underlying human type 2 diabetes mellitus. In all aspects studied to date the nonhuman primate has been shown to develop the same disease with the same features that develop in overweight middle-aged humans. This includes the progressive development of the known complications of diabetes, all of which are extraordinarily like those identified in humans. In addition, for the development and evaluation of new therapeutic agents, the translation of findings from nonhuman primates to application in humans has been highly predictable. Both therapeutic efficacy and identification of potential adverse responses can be effectively examined in nonhuman primates due to their great similarity to humans at the molecular, biochemical, and physiological levels. This chapter provides guidance for the development and management of a colony of monkeys with naturally occurring type 2 diabetes mellitus.

Maternal diet: a modulator for epigenomic regulation during development in nonhuman primates and humans

The importance of diet in health and disease has been well characterized in the past decades. Although the earlier focus of diet research was in the context of undernutrition and the importance of adequate nutrient intake to prevent malnutrition, in the current era of epidemic obesity the focus of our efforts has evolved toward understanding the effects of excess caloric intake. The current surge in childhood obesity rates suggests a correlation of maternal metabolic syndrome and obesity with programming of the fetal epigenome for metabolic diseases later in life. Alterations of the fetal genome, epigenome and metabolome have been well documented in cases of maternal malnutrition, including both overnutrition and undernutrition. It is of great interest and importance to understand how these divergent maternal factors regulate/program the fetus for metabolic diseases, and we and others have observed that epigenetic modifications to the fetal and placental epigenome accompany these reprogramming events. The following review summarizes recent studies on the effects of maternal diet and obesity on fetal epigenetics contributing to adult diseases later in life by taking advantage of state-of-the-art genomic, epigenomic and metagenomic techniques in nonhuman primate model systems.

The changes of glucose and lipid metabolism in overweight middle-aged cynomolgus monkeys

BACKGROUND

Excessive weight gain has been observed in middle-aged cynomolgus monkeys. This study was designed to investigate the metabolic characteristics in overweight monkeys.

METHODS

A total of 26 cynomolgus monkeys were grouped based on gender and body weight. Overweight was operationally defined as body weight heavier than 9.6 kg in males and 7.5 kg in females. They were monitored for glucose and insulin in fasting state, serum parameters, and somatometric measurements.

RESULTS

Higher measurements of weight, body mass index (BMI), waist, hip, and waist/hip ratio (WHR) were the somatometric characteristics of overweight monkeys. Abdominal fat deposition was more prominent in females. Elevated total cholesterol, HDL-C, LDL-C, and fasting glucose were observed in female overweight monkeys. Impaired insulin sensitivity occurred in overweight monkeys.

CONCLUSIONS

Overweight could result in impaired insulin sensitivity. The metabolic changes were more prominent in female overweight monkeys.

A preliminary report on the feeding of cynomolgus monkeys (Macaca fascicularis) with a high-sugar high-fat diet for 33 weeks

BACKGROUND

The metabolic syndrome is common in populations exposed to a typical Western diet. There is a lack of an animal model that mimics this condition.

METHODS

We fed 15 cynomolgus monkeys ad libitum a high-sugar high-fat (HSHF) diet for 33 weeks. Body weight, body composition, serum lipids, and insulin were measured at baseline and at 33 weeks.

RESULTS

The animals tolerated the HSHF diet very well. In the intervention group, total serum cholesterol and low-density lipoprotein cholesterol were 3- and 5-fold higher, respectively, at 33 weeks as compared with their baseline levels. Serum high-density lipoprotein cholesterol and triglycerides were not significantly affected. Dual-energy X-ray absorptiometry (DXA) analysis of the intervention group indicated that the trunk fat mass increased by 187% during this period.

CONCLUSIONS

Cynomolgus monkeys should be a useful model for investigating the interactions of diet and other factors such as genetics in the development of the metabolic syndrome.