Alterations of Fatty Acid Profile May Contribute to Dyslipidemia in Chronic Kidney Disease by Influencing Hepatocyte Metabolism

Association of plasma ceramide with decline in kidney function in patients with type 2 diabetes

Circulating ceramide levels are dysregulated in kidney disease. However, their associations with rapid decline in kidney function (RDKF) and end-stage kidney disease (ESKD) in patients with type 2 diabetes (T2D) are unknown. In this prospective study of 1746 T2D participants, we examined the association of plasma ceramide Cer16:0, Cer18:0, Cer24:0, and Cer24:1 with RDKF, defined as an estimated glomerular filtration rate (eGFR) decline of 5 ml/min/1.73 m2 per year or greater, and ESKD defined as eGFR <15/min/1.73 m2 for at least 3 months, on dialysis or renal death at follow-up. During a median follow-up period of 7.7 years, 197 patients experienced RDKF. Ceramide Cer24:0 (odds ratio [OR] = 0.71, 95% CI 0.56-0.90) and ratios Cer16:0/Cer24:0 (OR = 3.54 [1.70-7.35]), Cer18:0/Cer24:0 (OR = 1.89 [1.10-3.25]), and Cer24:1/Cer24:0 (OR = 4.01 [1.93-8.31]) significantly associated with RDKF in multivariable analysis; 124 patients developed ESKD. The ratios Cer16:0/Cer24:0 (hazard ratio [HR] = 3.10 [1.44-6.64]) and Cer24:1/Cer24:0 (HR = 4.66 [1.93-11.24]) significantly associated with a higher risk of ESKD. The Cer24:1/Cer24:0 ratio improved risk discrimination for ESKD beyond traditional risk factors by small but statistically significant margin (Harrell C-index difference: 0.01; P = 0.022). A high ceramide risk score also associated with RDKF (OR = 2.28 [1.26-4.13]) compared to lower risk score. In conclusion, specific ceramide levels and their ratios are associated with RDKF and conferred an increased risk of ESKD, independently of traditional risk factors, including baseline renal functions in patients with T2D.

Causal associations between polyunsaturated fatty acids and kidney function: A bidirectional Mendelian randomization study

BACKGROUND

PUFAs were suggested to be beneficial for kidney function in observational studies. However, whether these associations are causal remains unclear.

OBJECTIVES

This study explores the causality between PUFAs and chronic kidney disease (CKD) or estimated glomerular filtration rate (eGFR) using bidirectional 2-sample Mendelian randomization (MR).

METHODS

Single nucleotide polymorphisms associated with PUFAs and kidney function were obtained from the largest and most recent genome-wide association studies with sample sizes of 13,544, 13,506, 13,499, 13,527, and 13,549 for omega-3 fatty acids, omega-6 fatty acids, DHA, LA, and other PUFAs than 18:2 (otPUFA), and 480,698 and 1,201,909 for CKD and eGFR, respectively. MR inverse-variance weighted (IVW) and pleiotropy residual sum and outlier test (MR-PRESSO) were used for data analysis, supplemented with a weighted median estimator, MR-Egger regression, and multivariable MR, giving β or OR and their 95% CIs.

RESULTS

There was suggestive evidence that higher omega-6 fatty acids were associated with increased eGFR using MR-PRESSO [β: 0.005 log(mL/min/1.73 m²) per SD increase in omega-6 fatty acids; 95% CI: 0.002, 0.008; P = 0.008]. Higher LA level was also associated with higher eGFR [β: 0.005 log(mL/min/1.73 m²) per SD increase in LA; 95% CI: 0.003, 0.007; P = 0.0007] using MR-PRESSO. Neither association of the other PUFAs, i.e., omega-3 fatty acids, DHA, and otPUFA, with CKD or eGFR nor the association of CKD and eGFR with PUFAs was found. Similar results were found in sensitivity analyses.

CONCLUSIONS

Our results suggest that higher omega-6 fatty acids and LA may increase eGFR levels. Although the estimated effects were relatively small, the results provide public health and research relevance, indicating the need for further longitudinal cohorts or randomized controlled trials on omega-6 fatty acids in improving kidney function.

Combined association of triglyceride-glucose index and systolic blood pressure with all-cause and cardiovascular mortality among the general population

Background

The combined association of triglyceride-glucose (TyG) index and different systolic blood pressure (SBP) levels with all-cause and cardiovascular mortality among the general population remains unclear.

Methods

In this study, 6245 individuals were from the National Health and Nutrition Examination Survey (1999–2002). The study endpoints were all-cause and cardiovascular mortality. Multivariate Cox proportional hazards regression models were used to explore the combined association of TyG index and different SBP levels with all-cause and cardiovascular mortality.

Results

During a mean follow-up period of 66.8 months, a total of 284 all-cause deaths (331/100000 person-years) and 61 cardiovascular deaths (66/100000 person-years) were recorded. Multivariate Cox regression analysis revealed that the combination of low TyG index and low SBP (< 120 mmHg and < 130 mmHg) was associated with a reduced risk of all-cause and cardiovascular mortality than others. However, survival benefit was not observed in the combined group with the low TyG index and SBP < 140 mmHg. Furthermore, the mortality rate in the combined group of low TyG index and low SBP gradually increased with the elevation of SBP level.

Conclusion

The combination of low TyG index and low SBP (< 120 mmHg and < 130 mmHg) was associated with a lower risk of all-cause and cardiovascular mortality. However, no survival benefit was observed in the combined group of low TyG index and SBP < 140 mmHg.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03678-z.

Associations between Serum Saturated Fatty Acids Content and Mortality in Dialysis Patients

Background: Cardiovascular mortality in dialysis population remains very high. Saturated fatty acids (SFA) contribute to atherosclerosis and to cardiovascular risk. Aim: The aim of this study was to evaluate the relationship between mortality in dialysis patients and the serum SFA content. Methods: Survival of 54 patients on dialysis was assessed. A total of 21 SFA from patients’ sera were measured by gas chromatography-mass spectrometry (GC-MS). Diet was assessed by food frequency questionnaire FFQ-6. The SFA content is presented as fatty acid proportion (%). Results: During the observation time (median 66 months) 22 patients died. There was a significant relationship between elevated SFA (above SFA mean) and mortality (log-rank 3.13; p = 0.0017). Moreover, patients who ingested foods rich in SFA, according to FFQ-6, had a higher mortality risk (log-rank 2.24; p = 0.03). The hazard ratio for mortality associated with increased SFA content equalled 4.47 (1.63−12.26). Addition of age and inflammation (hsCRP > 5 mg/L) into the Cox model did not modify this relationship. However, SFA content turned out to be significantly higher in patients with diabetes mellitus and cardiovascular disease, as compared to patients free from these co-morbidities. Their addition to the model attenuated the relationship between SFA and mortality, making it statistically insignificant. Conclusion: The serum content of SFA turned out to be a strong predictor of mortality in dialysis patients. However, given the significant associations between SFA, DM, and CVD, interventional studies with controlled SFA intake are needed to evaluate the causal links between SFA, co-morbidities and survival.

Docosahexaenoic acid-acylated curcumin diester alleviates cisplatin-induced acute kidney injury by regulating the effect of gut microbiota on the lipopolysaccharide- and trimethylamine-N-oxide-mediated PI3K/Akt/NF-κB signaling pathway in mice

An increasing number of studies have reported the effects of curcumin (Cur) and docosahexaenoic acid (DHA) on alleviating acute kidney injury (AKI). In this work, we have performed a comparative investigation to determine the effect of dietary DHA-acylated Cur esters, ester derivatives of Cur, and recombination of curcumin and DHA on alleviating acute kidney injury in a mouse model induced by a single intraperitoneal injection with cisplatin (20 mg kg^-1). The results showed that the DHA-acylated Cur diesters significantly decreased the abnormally increased blood urea nitrogen, creatinine, lipopolysaccharide (LPS) and trimethylamine-N-oxide (TMAO) in serum caused by AKI. Histopathological results confirmed that DHA-acylated Cur diesters clearly reduced the degree of renal tubular injury. The renal protective effect of the DHA-acylated Cur diester was better than that of the monoester and the recombination of Cur and DHA. Notably, we found that the DHA-acylated Cur diester treatment remarkably changed the relative abundance of microbiota related to LPS and TMAO/trimethylamine (TMA) metabolism. Moreover, dietary DHA-acylated Cur diesters clearly reduced the MDA content and elevated GSH levels in the kidney of AKI mice, as well as changed the fatty acid composition in the kidney. Further mechanism studies showed that DHA-acylated Cur diesters significantly inhibited inflammation, apoptosis and oxidative stress by preventing the LPS and TMAO-mediated PI3K/Akt/NF-κB signaling pathway. The above results indicate that DHA-acylated Cur diesters are a potentially novel candidate or targeted dietary pattern to prevent and treat drug-induced acute kidney injury.

The Impact of Kidney Transplantation on the Serum Fatty Acid Profile in Patients with End-Stage Kidney Disease

Epidemiological data indicate that metabolic disturbances and increased cardiovascular risk in renal transplant patients are a significant and common problem. Therefore, it is important to search for new solutions and, at the same time, counteract the negative effects of currently used therapies. In this study, we examined the effect of kidney transplantation on the serum levels of fatty acids (FAs) in order to assess the role of these compounds in the health of transplant patients. The FA profile was analyzed by gas chromatography-mass spectrometry in the serum of 35 kidney transplant recipients, just before transplantation and 3 months later. The content of total n-3 polyunsaturated FAs (PUFAs) decreased after transplantation (3.06 ± 0.13% vs. 2.66 ± 0.14%; p < 0.05). The total amount of ultra-long-chain FAs containing 26 and more carbon atoms was significantly reduced (0.08 ± 0.009% vs. 0.05 ± 0.007%; p < 0.05). The desaturation index (18:1/18:0) increased after transplantation (3.92 ± 0.11% vs. 4.36 ± 0.18%; p < 0.05). The study showed a significant reduction in n-3 PUFAs in renal transplant recipients 3 months after transplantation, which may contribute to increased cardiovascular risk in this patient population.

Lipidomic approaches to dissect dysregulated lipid metabolism in kidney disease

Dyslipidaemia is a hallmark of chronic kidney disease (CKD). The severity of dyslipidaemia not only correlates with CKD stage but is also associated with CKD-associated cardiovascular disease and mortality. Understanding how lipids are dysregulated in CKD is, however, challenging owing to the incredible diversity of lipid structures. CKD-associated dyslipidaemia occurs as a consequence of complex interactions between genetic, environmental and kidney-specific factors, which to understand, requires an appreciation of perturbations in the underlying network of genes, proteins and lipids. Modern lipidomic technologies attempt to systematically identify and quantify lipid species from biological systems. The rapid development of a variety of analytical platforms based on mass spectrometry has enabled the identification of complex lipids at great precision and depth. Insights from lipidomics studies to date suggest that the overall architecture of free fatty acid partitioning between fatty acid oxidation and complex lipid fatty acid composition is an important driver of CKD progression. Available evidence suggests that CKD progression is associated with metabolic inflexibility, reflecting a diminished capacity to utilize free fatty acids through β-oxidation, and resulting in the diversion of accumulating fatty acids to complex lipids such as triglycerides. This effect is reversed with interventions that improve kidney health, suggesting that targeting of lipid abnormalities could be beneficial in preventing CKD progression.

Metabolic Reprogramming and Renal Fibrosis

There are several causes of chronic kidney disease, but all of these patients have renal fibrosis. Although many studies have examined the pathogenesis of renal fibrosis, there are still no effective treatments. A healthy and balanced metabolism is necessary for normal cell growth, proliferation, and function, but metabolic abnormalities can lead to pathological changes. Normal energy metabolism is particularly important for maintaining the structure and function of the kidneys because they consume large amounts of energy. We describe the metabolic reprogramming that occurs during renal fibrosis, which includes changes in fatty acid metabolism and glucose metabolism, and the relationship of these changes with renal fibrosis. We also describe the potential role of novel drugs that disrupt this metabolic reprogramming and the development of fibrosis, and current and future challenges in the treatment of fibrosis.

Zinc Deficiency, Plasma Fatty Acid Profile and Desaturase Activities in Hemodialysis Patients: Is Supplementation Necessary?

Background: Desaturation and elongation are critical processes in endogenous metabolic fatty acid pathways. Zinc (Zn) is a cofactor for desaturases and elongases enzymes. There is limited evidence regarding the relationships between biomarkers of Zn status, nutritional intake, plasma phospholipid fatty acid profile and clinical outcomes among patients undergoing hemodialysis (HD). Objective: To examine the relationships between dietary and serum levels of Zn and Cu/Zn ratio and to explore associations of these micronutrients with PUFA profile and estimated desaturase and elongase enzyme activities in serum phospholipids among HD patients. Methods: This study included 40 adult patients undergoing hemodialysis treatment. Repeated 24-h recalls were applied for dietary intake assessment. Serum concentration of Zn and Cu were determined using inductively coupled plasma mass spectrometry and fatty acid composition by gas-liquid chromatography. Desaturase and elongase activities were calculated from product-precursor fatty acid ratios. Results: Inadequate dietary Zn intake was found in 55% of HD patients. They all had serum Zn concentration below the reference value of 60 μg/dL (mean 38.8 ± 7.72 μg/dL). Adequate zinc intake was accompanied with significantly higher intake of energy, total fats, SFA, MUFA and proteins. There was no correlation between Zn serum status and Zn intake estimates. Serum Cu/Zn ratio was high, (2.76 ± 0.68), directly and significantly associated with HD period, CRP, BMI, VFA, and inversely with Kt/V, albumin, iron, and iPTH. The n-6/n-3 ratio in plasma phospholipids was elevated (12.25 ± 3.45) and patients with inadequate Zn intake had lower n-3 PUFA intake and status compared to those with adequate intake. Serum Zn concentrations were inversely correlated with linoleic/dihomo-γ-linolenic acid ratio (LA/DGLA) (p = 0.037), related to D6-desaturase activity (p = 0.033) and directly with DGLA relative abundances (p = 0.024). Cu status was inversely associated with EPA level (p = 0.03) and estimates of elongase activity (p = 0.001). Furthermore, positive relationship was found between the Cu/Zn ratio and determined elongase value (p = 0.01). Conclusion: Findings of this study underpin the high prevalence of Zn deficiency and inadequate n-3 PUFA intake and status among subjects undergoing HD. The results obtained indicate that the assessment of Zn status should be a standard parameter of nutritional status screening in HD patients while emphasizing the importance of Cu/Zn determination. Although further research is warranted, Zn and-n-3 PUFA supplementation in HD patients might be beneficial for the prevention and attenuation of adverse health outcomes.

Dietary Lipids and Dyslipidemia in Chronic Kidney Disease

The progression of chronic kidney disease (CKD) leads to altered lipid metabolism. CKD patients exhibit high blood triglyceride (TG) levels, reduced concentrations and functionality of high-density lipoproteins (HDL), and elevated levels of atherogenic small, dense, low-density lipoproteins (sdLDL). Disorders of lipid metabolism and other metabolic disturbances place CKD patients at high risk for cardiovascular disease (CVD). Extensive evidence supports the cardioprotective effects of unsaturated fatty acids, including their beneficial effect on serum cholesterol and TG levels. Dietary lipids might therefore be especially important in the nutritional management of CKD. We review current dietary recommendations for fat intake by CKD patients and suggest potential nutritional interventions by emphasizing dietary lipids that might improve the blood lipid profile and reduce cardiovascular risk in CKD.

Lipoproteins and fatty acids in chronic kidney disease: molecular and metabolic alterations

Chronic kidney disease (CKD) induces modifications in lipid and lipoprotein metabolism and homeostasis. These modifications can promote, modulate and/or accelerate CKD and secondary cardiovascular disease (CVD). Lipid and lipoprotein abnormalities - involving triglyceride-rich lipoproteins, LDL and/or HDL - not only involve changes in concentration but also changes in molecular structure, including protein composition, incorporation of small molecules and post-translational modifications. These alterations modify the function of lipoproteins and can trigger pro-inflammatory and pro-atherogenic processes, as well as oxidative stress. Serum fatty acid levels are also often altered in patients with CKD and lead to changes in fatty acid metabolism - a key process in intracellular energy production - that induce mitochondrial dysfunction and cellular damage. These fatty acid changes might not only have a negative impact on the heart, but also contribute to the progression of kidney damage. The presence of these lipoprotein alterations within a biological environment characterized by increased inflammation and oxidative stress, as well as the competing risk of non-atherosclerotic cardiovascular death as kidney function declines, has important therapeutic implications. Additional research is needed to clarify the pathophysiological link between lipid and lipoprotein modifications, and kidney dysfunction, as well as the genesis and/or progression of CVD in patients with kidney disease.

The Role of Fatty Acids in Non-Alcoholic Fatty Liver Disease Progression: An Update

Non-alcoholic fatty liver disease (NAFLD) is a major public health problem worldwide. NAFLD (both simple steatosis and steatohepatitis) is characterized by alterations in hepatic lipid metabolism, which may lead to the development of severe liver complications including cirrhosis and hepatocellular carcinoma. Thus, an exhaustive examination of lipid disorders in the liver of NAFLD patients is much needed. Mass spectrometry-based lipidomics platforms allow for in-depth analysis of lipid alterations in a number of human diseases, including NAFLD. This review summarizes the current research on lipid alterations associated with NAFLD and related complications, with special emphasis on the changes in long-chain and short-chain fatty acids levels in both serum and liver tissue, as well as in the hepatic expression of genes encoding the enzymes catalyzing lipid interconversions.

The Causes and Potential Injurious Effects of Elevated Serum Leptin Levels in Chronic Kidney Disease Patients

Leptin is an adipokine that regulates appetite and body mass and has many other pleiotropic functions, including regulating kidney function. Increased evidence shows that chronic kidney disease (CKD) is associated with hyperleptinemia, but the reasons for this phenomenon are not fully understood. In this review, we focused on potential causes of hyperleptinemia in patients with CKD and the effects of elevated serum leptin levels on patient kidney function and cardiovascular risk. The available data indicate that the increased concentration of leptin in the blood of CKD patients may result from both decreased leptin elimination from the circulation by the kidneys (due to renal dysfunction) and increased leptin production by the adipose tissue. The overproduction of leptin by the adipose tissue could result from: (a) hyperinsulinemia; (b) chronic inflammation; and (c) significant lipid disturbances in CKD patients. Elevated leptin in CKD patients may further deteriorate kidney function and lead to increased cardiovascular risk.

Analysis of Serum Fatty Acids Profile in Kidney Transplant Recipients

Patients with end-stage kidney disease, treated with renal transplantation, are at increased risk of cardio-vascular disease (CVD) and cardio-vascular mortality. They are also characterized by an atherogenic dyslipidemia. Alterations of the fatty acids (FA) profile contribute to increased cardio-vascular risk in the general population. In the current study we test the hypothesis that kidney transplantation is associated with ab-normalities in FA profile. FA profile was analysed by gas chromatography–mass spectrometry in 198 renal transplant recipients, and 48 control subjects. The most profound differences between renal transplant patients and controls were related to the content of branched chain FA, monounsaturated FA, and n-6 polyunsaturated FA, respectively. The FA profile significantly separated the patients from the controls in the principal component analysis (PCA). The abnormalities of FA profile showed a tendency for normalization in long-term kidney recipients, as compared to patients with recent transplants. The n-3 PUFA content demonstrated a strong inverse association with the presence of inflammation. Most profound alterations of the FA profile were observed in patients with impaired graft function (glomerular filtration rate < 45 mL/min). The study demonstrated significant disorders of the FA profile in kidney transplant recipients, that might contribute to cardio-vascular risk in this vulnerable patient population.

Machine Learning Approaches Reveal Metabolic Signatures of Incident Chronic Kidney Disease in Individuals With Prediabetes and Type 2 Diabetes

Early and precise identification of individuals with prediabetes and type 2 diabetes (T2D) at risk for progressing to chronic kidney disease (CKD) is essential to prevent complications of diabetes. Here, we identify and evaluate prospective metabolite biomarkers and the best set of predictors of CKD in the longitudinal, population-based Cooperative Health Research in the Region of Augsburg (KORA) cohort by targeted metabolomics and machine learning approaches. Out of 125 targeted metabolites, sphingomyelin C18:1 and phosphatidylcholine diacyl C38:0 were identified as candidate metabolite biomarkers of incident CKD specifically in hyperglycemic individuals followed during 6.5 years. Sets of predictors for incident CKD developed from 125 metabolites and 14 clinical variables showed highly stable performances in all three machine learning approaches and outperformed the currently established clinical algorithm for CKD. The two metabolites in combination with five clinical variables were identified as the best set of predictors, and their predictive performance yielded a mean area value under the receiver operating characteristic curve of 0.857. The inclusion of metabolite variables in the clinical prediction of future CKD may thus improve the risk prediction in people with prediabetes and T2D. The metabolite link with hyperglycemia-related early kidney dysfunction warrants further investigation.

Dyslipidemia in Kidney Disorders: Perspectives on Mitochondria Homeostasis and Therapeutic Opportunities

To excrete body nitrogen waste and regulate electrolyte and fluid balance, the kidney has developed into an energy factory with only second to the heart in mitochondrial content in the body to meet the high-energy demand and regulate homeostasis. Energy supply from the renal mitochondria majorly depends on lipid metabolism, with programed enzyme systems in fatty acid β-oxidation and Krebs cycle. Renal mitochondria integrate several metabolic pathways, including AMPK/PGC-1α, PPARs, and CD36 signaling to maintain energy homeostasis for dynamic and static requirements. The pathobiology of several kidney disorders, including diabetic nephropathy, acute and chronic kidney injuries, has been primarily linked to impaired mitochondrial bioenergetics. Such homeostatic disruption in turn stimulates a pathological adaptation, with mitochondrial enzyme system reprograming possibly leading to dyslipidemia. However, this alteration, while rescuing oncotic pressure deficit secondary to albuminuria and dissipating edematous disorder, also imposes an ominous lipotoxic consequence. Reprograming of lipid metabolism in kidney injury is essential to preserve the integrity of kidney mitochondria, thereby preventing massive collateral damage including excessive autophagy and chronic inflammation. Here, we review dyslipidemia in kidney disorders and the most recent advances on targeting mitochondrial energy metabolism as a therapeutic strategy to restrict renal lipotoxicity, achieve salutary anti-edematous effects, and restore mitochondrial homeostasis.

Increased Expression of the Leptin Gene in Adipose Tissue of Patients with Chronic Kidney Disease-The Possible Role of an Abnormal Serum Fatty Acid Profile

Chronic kidney disease (CKD) is associated with an increased level of leptin and an abnormal fatty acid (FA) profile in the serum. However, there are no data on the associations between them, and the reason for increased serum levels in patients with CKD is not well elucidated. Recently, we found that a CKD-related abnormal FA profile caused significant changes in the expression of genes involved in lipid metabolism in hepatocytes. The aim of this study was to examine whether leptin gene expression in subcutaneous adipose tissue (SAT) of patients with CKD may contribute to increased serum levels of this adipokine and whether the abnormal serum FA profile observed in CKD patients has an impact on leptin gene expression in adipocytes. The FA profile was measured in serum samples from patients with CKD and controls by GC–MS. The relative mRNA levels of leptin were measured in SAT by Real-Time PCR. Moreover, the effect of the CKD-related abnormal FA profile on leptin gene expression was studied in in vitro cultured 3T3-L1 adipocytes. Patients with CKD had higher concentrations of serum leptin than controls and higher expression level of the leptin gene in SAT. They also had increased serum monounsaturated FAs and decreased polyunsaturated FAs. The incubation of adipocytes with FAs isolated from CKD patients resulted in an increase of the levels of leptin mRNA. Increased leptin gene expression in SAT may contribute to elevated concentrations of these adipokine in patients with CKD. CKD-related alterations of the FA profile may contribute to elevated serum leptin concentrations in patients with CKD by increasing the gene expression of this adipokine in SAT.