Effect of a low-protein diet supplemented with ketoacids on skeletal muscle atrophy and autophagy in rats with type 2 diabetic nephropathy

Keto Acids Attenuate Skeletal Muscle Atrophy in Chronic Kidney Disease via Inhibiting Pyroptosis and Upregulating Irisin Precursor FNDC5 Expression

It is widely accepted that keto acids supplementation can protect skeletal muscle from atrophy. Pyroptosis has been considered to be one of the new mechanisms of muscle atrophy. This study aimed to explore the effects and mechanisms of keto acids supplementation on chronic kidney disease (CKD)-induced skeletal muscle atrophy. In vitro, C2C12 myoblast cells were treated with indoxyl sulfate (IS, 1 mM) and leucine (Leu, 0 ng/mL, 50 ng/mL or 100 ng/mL). In animal experiment, animals were divided into four groups: normal control (NC) group (wildtype mice), CKD group (wildtype mice with CKD modeling), keto acids (KAs) group (CKD wildtype mice treated with KA), and FNDC5-/- group (Fndc5 (irisin precursor) gene knockout mice with CKD modeling and KA treatment). Results showed that leucine improved IS-induced myotube atrophy, decreased percentage of Propidium Iodide (PI)-positive cells, upregulated FNDC5 expression levels, and downregulated the pyroptosis-related protein levels, such as NLRP3, cleaved CASP1, and GSDMD-N. KA supplementation improved renal function and skeletal muscle atrophy. Furthermore, KA supplementation suppressed the expression of pyroptosis-related proteins and increased the expression of FNDC5. However, Fndc5 gene knockout partially reversed the protective effects of keto acids in CKD. In conclusion, our results showed for the first time that KA supplementation improves CKD-induced skeletal muscle atrophy by inhibiting pyroptosis and increasing expression of irisin/FNDC5. Our findings provide a novel insight into the treatment of the CKD-induced skeletal muscle atrophy.

Low protein diet supplemented with ketoacids on muscle wasting in chronic kidney disease: A clinical trial

Aim

Nutrition is an important part of the care of patients with chronic kidney disease (CKD). However, there is limited clinical research on the skeletal muscle nutrition of patients with CKD. We carried out this study to find out whether a low-protein diet supplemented with ketoacids (LPD + KA) could improve muscle wasting in patients with CKD.

Methods

Patients were enrolled in this non-blind, parallel-group, randomized trial assessing the nutritional status of CKD, randomly assigned to either the LPD + KA group or conventional LPD group. Blood samples such as Hemoglobin, Cystatin C, Creatinine, BUN, Albumin, Pre- Albumin, Glycerin Trilaurate, and Cholesterol were measured at baseline and every 3 months. The parameters of skeletal muscle and other body composition were assessed before and after dietary intervention for 12 months.

Results

A total of 58 patients with CKD completed the study and were available for further analysis. The hemoglobin and albumin were observed to be markedly improved in the LPD + KA group during the follow-up as compared to baseline. Body mass index and total body water index of both groups were increased upon follow-up but the increase in the LPD + KA group was comparatively higher. Moreover, an increase in body fat%, skeletal muscle mass index, and appendicular skeletal muscle mass index was observed in both groups between baseline and follow-up, but it was statistically insignificant.

Conclusion

This study did not find a significant improvement of KAs on muscle wasting, and a long time or more indices study may need to find the effects of the LPD + KA diets.

Clinical trial registration

[www.ClinicalTrials.gov], identifier [NCT02568020].

Low Protein Diets and Plant-Based Low Protein Diets: Do They Meet Protein Requirements of Patients with Chronic Kidney Disease?

A low protein diet (LPD) has historically been used to delay uremic symptoms and decrease nitrogen (N)-derived catabolic products in patients with chronic kidney disease (CKD). In recent years it has become evident that nutritional intervention is a necessary approach to prevent wasting and reduce CKD complications and disease progression. While a 0.6 g/kg, high biological value protein-based LPD has been used for years, recent observational studies suggest that plant-derived LPDs are a better approach to nutritional treatment of CKD. However, plant proteins are less anabolic than animal proteins and amino acids contained in plant proteins may be in part oxidized; thus, they may not completely be used for protein synthesis. In this review, we evaluate the role of LPDs and plant-based LPDs on maintaining skeletal muscle mass in patients with CKD and examine different nutritional approaches for improving the anabolic properties of plant proteins when used in protein-restricted diets.

Muscle protein turnover and low-protein diets in patients with chronic kidney disease

Adaptation to a low-protein diet (LPD) involves a reduction in the rate of amino acid (AA) flux and oxidation, leading to more efficient use of dietary AA and reduced ureagenesis. Of note, the concept of 'adaptation' to low-protein intakes has been separated from the concept of 'accommodation', the latter term implying a decrease in protein synthesis, with development of wasting, when dietary protein intake becomes inadequate, i.e. beyond the limits of the adaptive mechanisms. Acidosis, insulin resistance and inflammation are recognized mechanisms that can increase protein degradation and can impair the ability to activate an adaptive response when an LPD is prescribed in a chronic kidney disease (CKD) patient. Current evidence shows that, in the short term, clinically stable patients with CKD Stages 3-5 can efficiently adapt their muscle protein turnover to an LPD containing 0.55-0.6 g protein/kg or a supplemented very-low-protein diet (VLPD) by decreasing muscle protein degradation and increasing the efficiency of muscle protein turnover. Recent long-term randomized clinical trials on supplemented VLPDs in patients with CKD have shown a very good safety profile, suggesting that observations shown by short-term studies on muscle protein turnover can be extrapolated to the long-term period.

Usefulness of Urinary Creatinine/Urea Nitrogen Ratio as Indicator of Body Protein Catabolism in Dogs Fed Low Protein Diets

Low protein diets (LPs) constitute a reportedly effective form of nutritional therapy for canine chronic kidney disease and cirrhosis. These diets have long been feared to result in reduced muscle mass due to protein catabolism. This adverse effect, however, remains largely unrecognized in veterinary medicine as there are no easily applicable catabolism indicators. Therefore, we focused on urinary creatinine, a metabolite of protein in the urine, and examined whether its ratio to urinary urea nitrogen (UCrn/UN) can be used to assess protein catabolism. In Experiment 1, we first consecutively fed seven healthy beagles an LP, standard protein (SP), and high protein (HP) diet for 1 week each and then measured the UCrn/UN ratio at 2-h intervals from fasting to 16 h post-prandially. We consequently found that the UCrn/UN ratio was significantly elevated in the LP pre-prandially and at all post-prandial measurement points (P < 0.01). No significant differences were observed between the SP and HP. Analysis of fasting plasma amino-acid concentrations revealed that the concentration of methionine was significantly lower in the LP than in the other diets (P < 0.05). Although the effects of this change in amino-acid concentration were unclear, the UCrn/UN ratio was considered having increased due to a deficiency in protein and/or amino acids during LP feeding. In Experiment 2, we continuously fed five healthy beagles an LP for 18 weeks and then measured the UCrn/UN ratio as described above. We also measured changes in body composition with computed tomography. At weeks 10 and 18, the fasting UCrn/UN ratio was significantly higher than it was prior to the start of the LP; however, post-prandially, the UCrn/UN ratio decreased to the point that the significant difference disappeared. Muscle mass decreased at weeks 10 and 18. These results suggest that the fasting UCrn/UN ratio could be used as an indicator of protein catabolism in LP feeding. Our experiments thus indicate that examination of potential increases in the UCrn/UN ratio 1 week after introduction of LP feeding to healthy dogs could enable detection of body protein catabolism in long-term feeding of LP before muscle breakdown occurs.

Dietary supplementation with ketoacids protects against CKD-induced oxidative damage and mitochondrial dysfunction in skeletal muscle of 5/6 nephrectomised rats

Background

A low-protein diet supplemented with ketoacids (LPD + KA) maintains the nutritional status of patients with chronic kidney disease (CKD). Oxidative damage and mitochondrial dysfunction associated with the upregulation of p66SHC and FoxO3a have been shown to contribute to muscle atrophy. This study aimed to determine whether LPD + KA improves muscle atrophy and attenuates the oxidative stress and mitochondrial damage observed in CKD rats.

Methods

5/6 nephrectomy rats were randomly divided into three groups and fed with either 22% protein (normal-protein diet; NPD), 6% protein (low-protein diets; LPD) or 5% protein plus 1% ketoacids (LPD + KA) for 24 weeks. Sham-operated rats with NPD intake were used as the control.

Results

KA supplementation improved muscle atrophy and function in CKD + LPD rats. It also reduced the upregulation of genes related to the ubiquitin-proteasome system and 26S proteasome activity, as well as protein and mitochondrial oxidative damage in the muscles of CKD + LPD rats. Moreover, KA supplementation prevented the drastic decrease in activities of mitochondrial electron transport chain complexes, mitochondrial respiration, and content in the muscles of CKD + LPD rats. Furthermore, KA supplementation reversed the elevation in p66Shc and FoxO3a expression in the muscles of CKD + LPD rats.

Conclusions

Our results showed that KA supplementation to be beneficial to muscle atrophy in CKD + LPD, which might be associated with improvement of oxidative damage and mitochondrial dysfunction through suppression of p66Shc and FoxO3a.

Effects of Low-Protein, and Supplemented Very Low-Protein Diets, on Muscle Protein Turnover in Patients With CKD

Introduction

Early studies have shown that patients with chronic kidney disease (CKD) are able to maintain nitrogen balance despite significantly lower protein intake, but how and to what extent muscle protein metabolism adapts to a low-protein diet (LPD) or to a supplemented very LPD (sVLPD) is still unexplored.

Methods

We studied muscle protein turnover by the forearm perfusion method associated with the kinetics of ²H-phenylalanine in patients with CKD: (i) in a parallel study in subjects randomized to usual diet (1.1 g protein/kg, n = 5) or LPD (0.55 g protein/kg, n = 6) (Protocol 1); (ii) in a crossover, self-controlled study in subjects on a 0.55 g/kg LPD followed by a sVLPD (0.45 g/kg + amino/ketoacids 0.1 g/kg, n = 6) (Protocol 2).

Results

As compared with a 1.1 g/kg containing diet, a 0.55 g/kg LPD induced the following: (i) a 17% to 40% decrease in muscle protein degradation and net protein balance, respectively, (ii) no change in muscle protein synthesis, (iii) a slight (by approximately 7%, P < 0.06) decrease in whole-body protein degradation, and (iv) an increase in the efficiency of muscle protein turnover. As compared with an LPD, an sVLPD induced the following: (i) no change in muscle protein degradation, and (ii) an approximately 50% decrease in the negative net protein balance, and an increase in the efficiency of muscle protein turnover.

Conclusion

The results of these studies indicate that in patients with CKD the adaptation of muscle protein metabolism to restrained protein intake can be obtained via combined responses of protein degradation and the efficiency of recycling of amino acids deriving from protein breakdown.

Low-protein diet supplemented with ketoacids delays the progression of diabetic nephropathy by inhibiting oxidative stress in the KKAy mice model

Diabetic nephropathy (DN) is a major cause of chronic kidney disease. We aimed to investigate the effect of the low-protein diets (LPD) supplemented with ketoacids (LPD+KA) in KKAy mice, an early type 2 DN model. KKAy mice were treated with normal protein diet (NPD), LPD or LPD+KA from 12 to 24 weeks of age. A period of 12-week treatment with LPD significantly reduced albuminuria as compared with that observed after NPD treatment. Treatment with LPD+KA further reduced albuminuria as compared with that observed with LPD treatment alone. Moreover, LPD treatment reduced mesangial expansion, thickness of glomerular basement membrane and the severity of the podocyte foot process effacement in KKAy mice; these effects were more pronounced in KKAy mice treated with LPD+KA. Both LPD and LPD+KA treatments slightly reduced total body weight, but had no significant effect on kidney weight and blood glucose concentrations when compared with NPD-treated KKAy mice. LPD treatment slightly attenuated oxidative stress in kidneys as compared with that observed in NPD-treated KKAy mice; however, LPD+KA treatment remarkably ameliorated oxidative stress in diabetic kidneys as shown by decreased malondialdehyde concentrations, protein carbonylation, nitrotyrosine expression and increased superoxide dismutase expression. Nutritional therapy using LPD+KA confers additional renal benefits as compared with those of LPD treatment alone in early type 2 DN through inhibition of oxidative stress.

Neuromuscular junctions (NMJs): ultrastructural analysis and nicotinic acetylcholine receptor (nAChR) subunit mRNA expression in offspring subjected to protein restriction throughout pregnancy

Protein restriction during gestation can alter the skeletal muscle phenotype of offspring; however, little is known with regard to whether this also affects the neuromuscular junction (NMJ), as muscle phenotype maintenance depends upon NMJ functional integrity. This study aimed to evaluate the effects of a low protein (6%) intake by dams throughout gestation on male offspring NMJ morphology and nicotinic acetylcholine receptor (nAChR) α1, γ and ε subunit expression in the soleus (SOL) and extensor digitorum longus (EDL) muscles. Four groups of male Wistar offspring rats were studied. The offspring of dams fed low-protein (6% protein, LP) and normal protein (17% protein, NP) diets were evaluated at 30 and 120 days of age, and the SOL and EDL muscles were collected for analysis. Morphological studies using transmission electron microscopy revealed that only SOL NMJs were affected in 30-day-old offspring in the LP group compared with the NP group. SOL NMJs exhibited fewer synaptic folds, the postsynaptic membranes were smooth and myelin figures were also frequently observed in the terminal axons. With regard to the expression of mRNAs encoding nAChR subunits, only 30-day-old LP offspring EDL muscles exhibited reduced α, γ and ε subunit expression compared with the NP group. In conclusion, our results demonstrate that a low-protein diet (6%) imposed throughout pregnancy impairs the expression of mRNAs encoding the nAChR α, γ and ε subunits in EDL NMJs and promotes morphological changes in SOL NMJs of 30-day-old offspring, indicating specific differences among muscle types following long-term maternal protein restriction.

Differential control of muscle mass in type 1 and type 2 diabetes mellitus

Diabetes mellitus--whether driven by insulin deficiency or insulin resistance--causes major alterations in muscle metabolism. These alterations have an impact on nutrient handling, including the metabolism of glucose, lipids, and amino acids, and also on muscle mass and strength. However, the ways in which the distinct forms of diabetes affect muscle mass differ greatly. The most common forms of diabetes mellitus are type 1 and type 2. Thus, whereas type 1 diabetic subjects without insulin treatment display a dramatic loss of muscle, most type 2 diabetic subjects show no changes or even an increase in muscle mass. However, the most commonly used rodent models of type 2 diabetes are characterized by muscle atrophy and do not mimic the features of the disease in humans in terms of muscle mass. In this review, we analyze the processes that are differentially regulated under these forms of diabetes and propose regulatory mechanisms to explain them.

Myostatin Activates the Ubiquitin-Proteasome and Autophagy-Lysosome Systems Contributing to Muscle Wasting in Chronic Kidney Disease

Our evidence demonstrated that CKD upregulated the expression of myostatin, TNF-α, and p-IkBa and downregulated the phosphorylation of PI3K, Akt, and FoxO3a, which were also associated with protein degradation and muscle atrophy. The autophagosome formation and protein expression of autophagy-related genes were increased in muscle of CKD rats. The mRNA level and protein expression of MAFbx and MuRF-1 were also upregulated in CKD rats, as well as proteasome activity of 26S. Moreover, activation of myostatin elicited by TNF-α induces C2C12 myotube atrophy via upregulating the expression of autophagy-related genes, including MAFbx and MuRF1 and proteasome subunits. Inactivation of FoxO3a triggered by PI3K inhibitor LY294002 prevented the myostatin-induced increase of expression of MuRF1, MAFbx, and LC3-II protein in C2C12 myotubes. The findings were further consolidated by using siRNA interference and overexpression of myostatin. Additionally, expression of myostatin was activated by TNF-α via a NF-κB dependent pathway in C2C12 myotubes, while inhibition of NF-κB activity suppressed myostatin and improved myotube atrophy. Collectively, myostatin mediated CKD-induced muscle catabolism via coordinate activation of the autophagy and the ubiquitin-proteasome systems.

Piwil 2 gene transfection changes the autophagy status in a rat model of diabetic nephropathy

This study aims to investigate effects of Piwil2 on autohpagy in a DN rat model. Sixty health SD rats were selected and divided into four group, including normal group, control, DN and Piwil2 therapy group. DN model (DN group) was established by injecting the streptozotocin (50 mg/kg) into rats. Piwil2 therapy group was injected with viral plasmid carrying Piwil2 mRNA to DN rats. The urinary protein concentrations were determined by placing the animals in individual metabolic cages for a timed urine collection every 8 weeks. Blood and soleus muscle samples were collected after animals were sacrificed. Blood glucose was examined by using commercial detection kits. Western blot assay was employed to examine expression of Beclin 1 and LC3 (LC3 I and LC3 II) protein. Results indicated that urinary protein levels were remarkably higher in DN group compared to Normal and Control group (P<0.05). Blood glucose values were also increased in DN group compared to Normal and Control group (P<0.05). Body weights decreased significantly in DN rats compared to Normal group and Control group (P<0.05). Expression of Beclin 1 protein and LC3 proteins was significantly decreased in DN group compared to Normal and Control group (P<0.05). However, Piwil2 transfection could enhance level of Beclin 1 and LC3 protein significantly compared to DN group. In conclusion, the Tiwil 2 mRNA transfection could obviously enhance the autophagy biomarker, including Beclin 1 and LC3 protein, which indicates that the Tiwil 2 treatment has improved the autophagy in diabetic nephropathy rats.

Insulin Resistance Is Not Associated with an Impaired Mitochondrial Function in Contracting Gastrocnemius Muscle of Goto-Kakizaki Diabetic Rats In Vivo

Insulin resistance, altered lipid metabolism and mitochondrial dysfunction in skeletal muscle would play a major role in type 2 diabetes mellitus (T2DM) development, but the causal relationships between these events remain conflicting. To clarify this issue, gastrocnemius muscle function and energetics were investigated throughout a multidisciplinary approach combining in vivo and in vitro measurements in Goto-Kakizaki (GK) rats, a non-obese T2DM model developing peripheral insulin resistant without abnormal level of plasma non-esterified fatty acids (NEFA). Wistar rats were used as controls. Mechanical performance and energy metabolism were assessed strictly non-invasively using magnetic resonance (MR) imaging and 31-phosphorus MR spectroscopy (31P-MRS). Compared with control group, plasma insulin and glucose were respectively lower and higher in GK rats, but plasma NEFA level was normal. In resting GK muscle, phosphocreatine content was reduced whereas glucose content and intracellular pH were both higher. However, there were not differences between both groups for basal oxidative ATP synthesis rate, citrate synthase activity, and intramyocellular contents for lipids, glycogen, ATP and ADP (an important in vivo mitochondrial regulator). During a standardized fatiguing protocol (6 min of maximal repeated isometric contractions electrically induced at a frequency of 1.7 Hz), mechanical performance and glycolytic ATP production rate were reduced in diabetic animals whereas oxidative ATP production rate, maximal mitochondrial capacity and ATP cost of contraction were not changed. These findings provide in vivo evidence that insulin resistance is not caused by an impairment of mitochondrial function in this diabetic model.