Age and sex as confounding factors in the relationship between cardiac mitochondrial function and type 2 diabetes in the Nile Grass rat

Circulating Citrate Is Reversibly Elevated in Patients with End-Stage Liver Disease: Association with All-Cause Mortality

Circulating citrate may serve as a proxy for mitochondrial dysfunction which plays a role in the progression of end-stage liver disease (ESLD). This study aimed to determine the extent of alterations in circulating citrate in patients with ESLD, and examined its association with all-cause mortality among ESLD patients while on the waiting list for liver transplantation. Plasma citrate levels were measured using nuclear magnetic resonance spectroscopy in 129 ESLD patients (TransplantLines cohort study; NCT03272841) and compared to levels in 4837 participants of the community-dwelling PREVEND cohort. Plasma citrate levels were 40% higher in ESLD patients compared to PREVEND participants (p < 0.001). In a subset of 30 ESLD patients, citrate decreased following liver transplantation (p < 0.001), resulting in levels that were slightly lower than those observed in PREVEND participants. In multivariable analysis, plasma citrate levels were positively associated with Child-Turcotte-Pugh classification and inversely associated with estimated glomerular filtration rate (both p < 0.05). Survival was significantly reduced in ESLD patients in the highest citrate tertile (log-rank p = 0.037). Elevated citrate levels were associated with an increased risk of all-cause mortality in ESLD patients (HR per 1 Ln SD increment: 1.65 [95% CI: 1.03-2.63], p = 0.037). This association was suggested to be particularly present in men (HR: 2.04 [95% CI: 1.08-3.85], p = 0.027). In conclusion, plasma citrate levels are elevated in ESLD patients and decrease following liver transplantation. Moreover, elevated plasma citrate levels may be associated with increased all-cause mortality in ESLD patients, likely more pronounced in men.

Insulin and circadian rhythm genes of the Nile rat (Arvicanthis niloticus) are conserved and orthologous to those in the rat, mouse and human

The African grass or Nile rat (NR) (Arvicanthis niloticus) is a herbivorous diurnal rodent which is used as a biological model for research on type 2 diabetes mellitus (T2DM) and the circadian rhythm. Similar to humans, male NRs develop T2DM with high-carbohydrate diets. The NR thus provides a unique opportunity to identify the nutritional and underlying genetic factors that characterise human T2DM, as well as the effects of potential anti-diabetic phytochemicals such as Water-Soluble Palm Fruit Extract. Whole genome sequencing (WGS) could help identify possible genetic causes why NRs spontaneously develop T2DM in captivity. In this study, we performed WGS on a hepatic deoxyribonucleic acid (DNA) sample isolated from a male NR using PacBio high-fidelity long-read sequencing. The WGS data obtained were then de novo assembled and annotated using PacBio HiFi isoform sequencing (Iso-Seq) data as well as previous Illumina RNA sequencing (RNA-Seq) data. Genes related to insulin and circadian rhythm pathways were present in the NR genome, similar to orthologues in the rat, mouse and human genomes. T2DM development in the NR is thus most likely not attributable to structural differences in these genes when compared to other biological models. Further studies are warranted to gain additional insights on the genetic-environmental factors which underlie the genetic permissiveness of NRs to develop T2DM.

Plasma Citrate Levels Are Associated with an Increased Risk of Cardiovascular Mortality in Patients with Type 2 Diabetes (Zodiac-64)

Circulating citrate may represent a proxy of mitochondrial dysfunction which plays a role in the development of vascular complications in type 2 diabetes (T2D). Here, we determined the associations between plasma citrate levels and cardiovascular (CV) mortality in T2D patients. In this prospective cohort study, 601 patients were included who participated in the Zwolle Outpatient Diabetes project Integrating Available Care (ZODIAC). Plasma citrate levels were measured by nuclear magnetic resonance spectroscopy. Cox proportional hazards regression models were used to evaluate the associations between plasma citrate and the risk of CV mortality. Over a median follow-up of 11.4 years, 119 (19.8%) of the 601 patients died from a CV cause. In multivariable Cox proportional hazards regression models, adjusting for conventional risk factors, plasma citrate was associated with an increased risk of CV mortality (the hazard ratio (HR) per 1-SD increment was 1.19 (95%CI: 1.00-1.40), p = 0.048). This association was prominent in males (n = 49 with CV mortality) (HR 1.52 (95%CI: 1.14-2.03), p = 0.005), but not in females (n = 70 with CV mortality) (HR 1.11 (95%CI: 0.90-1.37), p = 0.319) (age-adjusted Pinteraction = 0.044). In conclusion, higher plasma citrate levels are associated with an increased risk of CV mortality in patients with established T2D. Future studies are warranted to unravel the potential role of citrate-related pathways in the pathogenesis of T2D-related vascular complications.

A systematic review on renal effects of SGLT2 inhibitors in rodent models of diabetic nephropathy

We have performed a systematic review of studies reporting on the renal effects of SGLT2 inhibitors in rodent models of diabetes. In 105 studies, SGLT2 inhibitors improved not only the glycemic control but also various aspects of renal function in most cases. These nephroprotective effects were similarly reported whether treatment with the SGLT2 inhibitor started concomitant with the onset of diabetes (within 1 week), early after onset (1-4 weeks) or after nephropathy had developed (>4 weeks after onset) with the latter probably having the greatest translational value. They were observed across various animal models of type 1 and type 2 diabetes/obesity (4 and 23 models, respectively), although studies in the type 2 diabetes model of db/db mice more often had negative data than in other models. Among possibly underlying pathophysiological mechanisms of nephroprotection, treatment with SGLT2 inhibitors had beneficial effects on lipid metabolism, blood pressure, glomerulosclerosis as well as renal tubular fibrosis, apoptosis, oxidative stress, and inflammation. These pathomechanisms highly influence atherosclerosis and renal health, which are two major factors that lead to an enhanced mortality in patients with diabetes and/or chronic kidney disease. Interestingly, renal SGLT2 inhibitor effects did not always correlate with those on glucose homeostasis, particularly in a limited number of direct comparative studies with other anti-diabetic treatments, indicating that nephroprotection may at least partly occur by mechanisms other than improving glycemic control. Our analyses did not provide evidence for different nephroprotective efficacy between SGLT2 inhibitors. Importantly, only four of 105 studies reported on female animals, and none provided direct comparative data between sexes. We conclude that more data on female animals and more direct comparative studies with other anti-diabetic compounds and combinations of treatments are needed.

Circulating Citrate Is Associated with Liver Fibrosis in Nonalcoholic Fatty Liver Disease and Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is associated with mitochondrial damage. Circulating mitochondrial metabolites may be elevated in NAFLD but their associations with liver damage is not known. This study aimed to assess the association of key mitochondrial metabolites with the degree of liver fibrosis in the context of NAFLD and nonalcoholic steatohepatitis (NASH). Cross-sectional analyses were performed on two cohorts of biopsy-proven NAFLD and/or NASH subjects. The association of circulating mitochondrial metabolite concentrations with liver fibrosis was assessed using linear regression analysis. In the single-center cohort of NAFLD subjects (n = 187), the mean age was 54.9 ±13.0 years, 40.1% were female and 86.1% were White. Type 2 diabetes (51.3%), hypertension (43.9%) and obesity (72.2%) were prevalent. Those with high citrate had a higher proportion of moderate/significant liver fibrosis (stage F ≥ 2) (68.4 vs. 39.6%, p = 0.001) and advanced fibrosis (stage F ≥ 3) (31.6 vs. 13.6%, p = 0.01). Citrate was associated with liver fibrosis independent of age, sex, NAFLD activity score and metabolic syndrome (per 1 SD increase: β = 0.19, 95% CI: 0.03-0.35, p = 0.02). This association was also observed in a cohort of NASH subjects (n = 176) (β = 0.21, 95% CI: 0.07-0.36, p = 0.005). The association of citrate with liver fibrosis was observed in males (p = 0.005) but not females (p = 0.41). In conclusion, circulating citrate is elevated and associated with liver fibrosis, particularly in male subjects with NAFLD and NASH. Mitochondrial function may be a target to consider for reducing the progression of liver fibrosis and NASH.

A comparison of urinary bladder weight in male and female mice across five models of diabetes and obesity

Introduction: Diabetes often leads to lower urinary tract dysfunction. The most frequently assessed parameter of urinary bladder dysfunction in animal models of diabetes is an enlargement of the bladder, which is consistently observed in type 1 and less consistently in type 2 diabetes. The vast majority of studies on bladder weight in animal models of diabetes and obesity has been performed in males, and no studies have directly compared this outcome parameter between sexes. Methods: Therefore, we have compared bladder weight and bladder/body weight ratio in five mouse models of obesity and diabetes (RIP-LCMV, db/db, ob/ob (two studies), insulin receptor substrate 2 (IRS2) knock-out mice and mice on a high-fat diet; pre-specified secondary analysis of a previously reported study). Results: In a pooled analysis of the control groups of all studies, females exhibited slightly lower glucose levels, lower body weight, and lower bladder weight, but bladder/body weight ratio was similar in both sexes (0.957 vs. 0.986 mg/g, mean difference 0.029 [-0.06; 0.118]). Among the six diabetic/obese groups, bladder/body weight ratio was similar in both sexes in three but smaller in female mice in three other groups. The mRNA expression of a panel of genes implied in the pathophysiology of bladder enlargement and/or fibrosis and inflammation did not differ systematically between sexes. Conclusions: We conclude that sex differences in diabetes/obesity-associated bladder enlargement may be model dependent.

Sex Differences in Glucose Homeostasis

Sexual dimorphism has been demonstrated to have an effect on various physiological functions. In this regard, researchers have investigated its impact on glucose homeostasis in both preclinical and clinical studies. Sex differences mainly arise from physiological factors such as sex hormones, body fat and muscle distribution, and sex chromosomes. The sexual dimorphism has also been studied in the context of diabetes. Reflecting the prevalence of the disease among the population, studies focusing on the sex difference in type 1 diabetes (T1D) are not common as the ones in type 2 diabetes (T2D). T1D is reported as the only major specific autoimmune disease that exhibits a male predominance. Clinical studies have demonstrated that impaired fasting glucose is more frequent in men whereas women more commonly exhibit impaired glucose tolerance. Understanding the sex difference in glucose homeostasis becomes more attractive when focusing on the findings that highlight sexual dimorphism on the efficacy or adverse effect profile of antidiabetic medications. Thus, in this chapter, we aimed to discuss the impact of sex on the glucose homeostasis both in health and in diabetes.

Multi-Tissue Time-Domain NMR Metabolomics Investigation of Time-Restricted Feeding in Male and Female Nile Grass Rats

Metabolic disease resulting from overnutrition is prevalent and rapidly increasing in incidence in modern society. Time restricted feeding (TRF) dietary regimens have recently shown promise in attenuating some of the negative metabolic effects associated with chronic nutrient stress. The purpose of this study is to utilize a multi-tissue metabolomics approach using nuclear magnetic resonance (NMR) spectroscopy to investigate TRF and sex-specific effects of high-fat diet in a diurnal Nile grass rat model. Animals followed a six-week dietary protocol on one of four diets: chow ad libitum, high-fat ad libitum (HF-AD), high-fat early TRF (HF-AM), or high-fat late TRF (HF-PM), and their liver, heart, and white adipose tissues were harvested at the end of the study and were analyzed by NMR. Time-domain complete reduction to amplitude–frequency table (CRAFT) was used to semi-automate and systematically quantify metabolites in liver, heart, and adipose tissues while minimizing operator bias. Metabolite profiling and statistical analysis revealed lipid remodeling in all three tissues and ectopic accumulation of cardiac and hepatic lipids for HF-AD feeding compared to a standard chow diet. Animals on TRF high-fat diet had lower lipid levels in the heart and liver compared to the ad libitum group; however, no significant differences were noted for adipose tissue. Regardless of diet, females exhibited greater amounts of hepatic lipids compared to males, while no consistent differences were shown in adipose and heart. In conclusion, this study demonstrates the feasibility of performing systematic and time-efficient multi-tissue NMR metabolomics to elucidate metabolites involved in the crosstalk between different metabolic tissues and provides a more holistic approach to better understand the etiology of metabolic disease and the effects of TRF on metabolic profiles.

Targeting NAD+: is it a common strategy to delay heart aging?

Heart aging is the main susceptible factor to coronary heart disease and significantly increases the risk of heart failure, especially when the aging heart is suffering from ischemia-reperfusion injury. Numerous studies with NAD+ supplementations have suggested its use in anti-aging treatment. However, systematic reviews regarding the overall role of NAD+ in cardiac aging are scarce. The relationship between NAD+ signaling and heart aging has yet to be clarified. This review comprehensively summarizes the current studies on the role of NAD+ signaling in delaying heart aging from the following aspects: the influence of NAD+ supplementations on the aging heart; the relationship and cross-talks between NAD+ signaling and other cardiac aging-related signaling pathways; Importantly, the therapeutic potential of targeting NAD+ in delaying heart aging will be discussed. In brief, NAD+ plays a vital role in delaying heart aging. However, the abnormalities such as altered glucose and lipid metabolism, oxidative stress, and calcium overload could also interfere with NAD+ function in the heart. Therefore, the specific physiopathology of the aging heart should be considered before applying NAD+ supplementations. We believe that this article will help augment our understanding of heart aging mechanisms. In the meantime, it provides invaluable insights into possible therapeutic strategies for preventing age-related heart diseases in clinical settings.

Early Time-Restricted Feeding Amends Circadian Clock Function and Improves Metabolic Health in Male and Female Nile Grass Rats

Lengthening the daily eating period contributes to the onset of obesity and metabolic syndrome. Dietary approaches, including energy restriction and time-restricted feeding, are promising methods to combat metabolic disorders. This study explored the effect of early and late time-restricted feeding (TRF) on weight and adiposity, food consumption, glycemic control, clock gene expression, and liver metabolite composition in diurnal Nile grass rats (NGRs). Adult male and female Nile grass rats were randomly assigned to one of three groups: (1) access to a 60% high-fat (HF) diet ad-libitum (HF-AD), (2) time-restricted access to the HF diet for the first 6 h of the 12 h light/active phase (HF-AM) or (3) the second 6 h of the 12 h light/active phase (HF-PM). Animals remained on their respective protocols for six weeks. TRF reduced total energy consumption and weight gain, and early TRF (HF-AM) reduced fasting blood glucose, restored Per1 expression, and reduced liver lipid levels. Although sex-dependent differences were observed for fat storage and lipid composition, TRF improved metabolic parameters in both male and female NGRs. In conclusion, this study demonstrated that early TRF protocol benefits weight management, improves lipid and glycemic control, and restores clock gene expression in NGRs.

Plasma acylcarnitine and diabetic retinopathy: A study from Eastern China

BACKGROUND AND PURPOSE

Acylcarnitines (ACars) are important for insulin resistance and type 2 diabetes (T2D). However, their roles in diabetic retinopathy (DR) remain controversial. In this study, we aimed to investigate the association of ACars with DR and their values in DR detection.

METHODS

This was a two-center case-control study based on the propensity score matching approach between August 2017 to June 2018 in Eastern China. Multivariable logistic regression models were applied to estimate the association of plasma ACars with DR. Differential ACars were screened by models of least absolute shrinkage and selection operator, elastic net, and weighted quantile sum regression, and their roles in DR identification were further evaluated by the area under the receiver operating curve (AUC).

RESULTS

Eight of twenty plasma ACars (8:0, 12:0, 12:1, 14:1, 16:2, 18:0, 18:2 and 18:3) were associated with DR, while only ACar 8:0 was selected by three variable selection methods. As compared to those with the 1^st tertile of ACar 8:0, the adjusted odds ratio (OR) and 95% confidence interval (CI) of DR were 0.22 (0.08, 0.59) and 0.12 (0.04, 0.36) for subjects in the 2^nd and 3^rd tertiles, respectively (P for trend < 0.001). Consistent associations were also observed in both restricted cubic spline regression models and subgroup analyses. AUC (95% CI) were 0.74 (0.66, 0.82) for ACar 8:0 alone and 0.77 (0.70, 0.85) for ACar 8:0 combined with covariates.

CONCLUSIONS

Our findings suggest higher ACar 8:0 is significantly associated with a decreased risk of DR, which provides a unique window for early identification of DR.

Nanoparticle-encapsulated antioxidant improves placental mitochondrial function in a sexually dimorphic manner in a rat model of prenatal hypoxia

Pregnancy complications associated with prenatal hypoxia lead to increased placental oxidative stress. Previous studies suggest that prenatal hypoxia can reduce mitochondrial respiratory capacity and mitochondrial fusion, which could lead to placental dysfunction and impaired fetal development. We developed a placenta-targeted treatment strategy using a mitochondrial antioxidant, MitoQ, encapsulated into nanoparticles (nMitoQ) to reduce placental oxidative stress and (indirectly) improve fetal outcomes. We hypothesized that, in a rat model of prenatal hypoxia, nMitoQ improves placental mitochondrial function and promotes mitochondrial fusion in both male and female placentae. Pregnant rats were treated with saline or nMitoQ on gestational day (GD) 15 and exposed to normoxia (21% O₂ ) or hypoxia (11% O₂ ) from GD15-21. On GD21, male and female placental labyrinth zones were collected for mitochondrial respirometry assessments, mitochondrial content, and markers of mitochondrial biogenesis, fusion and fission. Prenatal hypoxia reduced complex IV activity and fusion in male placentae, while nMitoQ improved complex IV activity in hypoxic male placentae. In female placentae, prenatal hypoxia decreased respiration through the S-pathway (complex II) and increased N-pathway (complex I) respiration, while nMitoQ increased fusion in hypoxic female placentae. No changes in mitochondrial content, biogenesis or fission were found. In conclusion, nMitoQ improved placental mitochondrial function in male and female placentae from fetuses exposed to prenatal hypoxia, which may contribute to improved placental function. However, the mechanisms (ie, changes in mitochondrial respiratory capacity and mitochondrial fusion) were distinct between the sexes. Treatment strategies targeted against placental oxidative stress could improve placental mitochondrial function in complicated pregnancies.