Lower levels of total HDL and HDL3 cholesterol are associated with albuminuria in normoalbuminuric Type 1 diabetic patients

High-Density Lipoproteins in Kidney Disease

Decades of epidemiological studies have established the strong inverse relationship between high-density lipoprotein (HDL)-cholesterol concentration and cardiovascular disease. Recent evidence suggests that HDL particle functions, including anti-inflammatory and antioxidant functions, and cholesterol efflux capacity may be more strongly associated with cardiovascular disease protection than HDL cholesterol concentration. These HDL functions are also relevant in non-cardiovascular diseases, including acute and chronic kidney disease. This review examines our current understanding of the kidneys’ role in HDL metabolism and homeostasis, and the effect of kidney disease on HDL composition and functionality. Additionally, the roles of HDL particles, proteins, and small RNA cargo on kidney cell function and on the development and progression of both acute and chronic kidney disease are examined. The effect of HDL protein modification by reactive dicarbonyls, including malondialdehyde and isolevuglandin, which form adducts with apolipoprotein A-I and impair proper HDL function in kidney disease, is also explored. Finally, the potential to develop targeted therapies that increase HDL concentration or functionality to improve acute or chronic kidney disease outcomes is discussed.

Efficacy of Caffeic Acid on Diabetes and Its Complications in the Mouse

Diabetic dyslipidemia and hyperglycemia contribute to excessive reactive oxygen species (ROS) production, leading to deleterious complications, such as nephropathy, atherosclerosis and cardiac dysfunction, and target major organs in the body. The aim of this study was to investigate the effect of caffeic acid (CA) on mouse weight and survival, serum level of fasting blood glucose (FBG), serum lipid parameters and atherogenic indices, oxidative damage in blood, liver and kidney tissue, pathophysiological changes and their function markers in healthy and alloxan-induced type 1 diabetic mice. Diabetes was induced in mice with a single intravenous injection of alloxan (75 mg kg⁻¹). Two days later, CA (50 mg kg⁻¹) was given intraperitoneally for seven days in diabetic mice. Diabetes affected glucose level, lipid profile, hematological and biochemical parameters, induced DNA damage and apoptotic/necrotic death in whole blood cells, liver and kidney, leading to weight loss and a decreased lifespan. CA treatment of diabetic mice revealed a protective effect on the liver and kidney, hypoglycemic and hypolipidemic properties and high protection against atherogenic outcomes. The obtained results suggest that CA is a safe and potent agent against diabetes that acts as an effective antioxidant in reducing serum glucose, lipid profile and atherogenic indices, leading to increased lifespan in mice.

Lipoprotein modulation of proteinuric renal injury

High-density lipoprotein (HDL) and its main protein, apolipoprotein AI (apoAI), have established benefits in various cells, but whether these cytoprotective effects of HDL pertain to renal cells is unclear. We investigated the in vitro consequences of exposing damaged podocytes to normal apoAI, HDL, and apoAI mimetic (L-4F), and the in vivo effects of L-4F on kidney and atherosclerotic injury in a podocyte-specific injury model of proteinuria. In vitro, primary mouse podocytes were injured by puromycin aminonucleoside (PAN). Cellular viability, migration, production of reactive oxygen species (ROS), apoptosis, and the underlying signaling pathway were assessed. In vivo, we used a proteinuric model, Nphs1-hCD25 transgenic (NEP25⁺) mice, which express human CD25 on podocytes. Podocyte injury was induced by using immunotoxin (LMB2) and generated a proteinuric atherosclerosis model, NEP25⁺:apoE^-/- mice, was generated by mating apoE-deficient (apoE^-/-) mice with NEP25⁺ mice. Animals received L-4F or control vehicle. Renal function, podocyte injury, and atherosclerosis were assessed. PAN reduced podocyte viability, migration, and increased ROS production, all significantly lessened by apoAI, HDL, and L-4F. L-4F attenuated podocyte apoptosis and diminished PAN-induced inactivation of Janus family protein kinase-2/signal transducers and activators of transcription 3. In NEP25⁺ mice, L-4F significantly lessened overall proteinuria, and preserved podocyte expression of synaptopodin and cell density. Proteinuric NEP25⁺:apoE^-/- mice had more atherosclerosis than non-proteinuric apoE^-/- mice, and these lesions were significantly decreased by L-4F. Normal human apoAI, HDL, and apoAI mimetic protect against podocyte damage. ApoAI mimetic provides in vivo beneficial effects on podocytes that culminate in reduced albuminuria and atherosclerosis. The results suggest supplemental apoAI/apoAI mimetic may be a novel candidate to lessen podocyte damage and its complications.

Kidneys: key modulators of high-density lipoprotein levels and function

PURPOSE OF REVIEW

The review will examine advances in our understanding of the role kidneys play in high-density lipoprotein (HDL) metabolism and the effect on levels, composition, and function of HDL particles.

RECENT FINDINGS

Components of the HDL particles can cross the glomerular filtration barrier. Some of these components, including apolipoproteins and enzymes involved in lipid metabolism, are taken up by the proximal tubule and degraded, modified, salvaged/returned to the circulation, or lost in the urine. Injury of the glomerular capillaries or tubules can affect these intrarenal processes and modify HDL. Changes in the plasma and urine levels of HDL may be novel markers of kidney damage or mechanism(s) of kidney disease.

SUMMARY

The kidneys have a significant role in the metabolism of individual HDL components, which in turn modulate HDL levels, composition, and functionality of HDL particles. These intrarenal effects may be useful markers of kidney damage and have consequences on kidney-related perturbations in HDL.

Increased HDL Size and Enhanced Apo A-I Catabolic Rates Are Associated With Doxorubicin-Induced Proteinuria in New Zealand White Rabbits

The catabolism and structure of high-density lipoproteins (HDL) may be the determining factor of their atheroprotective properties. To better understand the role of the kidney in HDL catabolism, here we characterized HDL subclasses and the catabolic rates of apo A-I in a rabbit model of proteinuria. Proteinuria was induced by intravenous administration of doxorubicin in New Zealand white rabbits (n = 10). HDL size and HDL subclass lipids were assessed by electrophoresis of the isolated lipoproteins. The catabolic rate of HDL-apo A-I was evaluated by exogenous radiolabelling with iodine-131. Doxorubicin induced significant proteinuria after 4 weeks (4.47 ± 0.55 vs. 0.30 ± 0.02 g/L of protein in urine, P < 0.001) associated with increased uremia, creatininemia, and cardiotoxicity. Large HDL2b augmented significantly during proteinuria, whereas small HDL3b and HDL3c decreased compared to basal conditions. HDL2b, HDL2a, and HDL3a subclasses were enriched with triacylglycerols in proteinuric animals as determined by the triacylglycerol-to-phospholipid ratio; the cholesterol content in HDL subclasses remained unchanged. The fractional catabolic rate (FCR) of [(131)I]-apo A-I in the proteinuric rabbits was faster (FCR = 0.036 h(-1)) compared to control rabbits group (FCR = 0.026 h(-1), P < 0.05). Apo E increased and apo A-I decreased in HDL, whereas PON-1 activity increased in proteinuric rabbits. Proteinuria was associated with an increased number of large HDL2b particles and a decreased number of small HDL3b and 3c. Proteinuria was also connected to an alteration in HDL subclass lipids, apolipoprotein content of HDL, high paraoxonase-1 activity, and a rise in the fractional catabolic rate of the [(131)I]-apo A-I.

Cubilin maintains blood levels of HDL and albumin

Cubilin is an endocytic receptor highly expressed in renal proximal tubules, where it mediates uptake of albumin and filtered forms of apoA-I/HDL. Cubilin deficiency leads to urinary loss of albumin and apoA-I; however, the consequences of cubilin loss on the homeostasis of blood albumin and apoA-I/HDL have not been studied. Using mice heterozygous for cubilin gene deletion (cubilin HT mice), we show that cubilin haploinsufficiency leads to reduced renal proximal tubular uptake of albumin and apoA-I and significantly increased urinary loss of albumin and apoA-I. Moreover, cubilin HT mice displayed significantly decreased blood levels of albumin, apoA-I, and HDL. The levels of albumin and apoA-I protein or mRNA expressed in the liver, kidney, or intestine of cubilin HT mice did not change significantly. The clearance rate of small HDL3 particles (density>1.13 g/ml) from the blood increased significantly in cubilin HT mice. In contrast, the rate of clearance of larger HDL2 particles from the blood did not change significantly, indicating a decreased half-life for HDL particles capable of filtering through the glomerulus. On the basis of these findings, we conclude that cubilin deficiency reduces renal salvage and delivery back to the blood of albumin and apoA-I, which decreases blood levels of albumin and apoA-I/HDL. These findings raise the possibility that therapeutic increase of renal cubilin expression might reduce proteinuria and increase blood levels of albumin and HDL.

Relationship between Adiponectin Level, Insulin Sensitivity, and Metabolic Syndrome in Type 1 Diabetic Patients

Objective. Adiponectin is known to be decreased in insulin resistance (IR) and metabolic syndrome (MS) which can be present in patients with type 1 diabetes mellitus (T1DM). The aim of this study was to evaluate the relationship between adiponectin level, MS, and insulin sensitivity in T1DM. Research Design and Methods. The study included 77 T1DM patients divided into two groups based on the total plasma adiponectin median value. Insulin sensitivity was calculated with the equation for eGDR, and MS was defined according to International Diabetes Federation criteria. Results. Patients with higher adiponectin level (n = 39) had significantly lower waist circumference (P < 0.002), fasting venous glucose levels (P < 0.001), higher HDL3-cholesterol (P = 0.011), and eGDR (P = 0.003) in comparison to the group with lower adiponectin who showed higher prevalence of MS (P = 0.045). eGDR increased for 1.09 mg/kg(-1) min(-1) by each increase of 1  µ g/mL total fasting plasma adiponectin (P = 0.003). In the logistic regression model, adiponectin was inversely associated with the presence of MS (P = 0.014). Conclusion. Higher adiponectin concentration is associated with lower prevalence of MS in T1DM. Whether higher adiponectin concentration has a protective role in the development of the MS in T1DM needs to be clarified in future follow-up studies.