Albumin modification and fragmentation in renal disease

Association between nocturia and serum albumin in the U.S. adults from NHANES 2005-2012

BACKGROUND

Nocturia, a prevalent chronic condition, impacts individuals' quality of life but remains underexplored. This study aimed to assess the association between serum albumin levels and nocturia.

METHODS

Based on the analysis of the National Health and Nutrition Examination Survey (NHANES) database (2005-2012), our study included a total of 6345 adults (≥20 years old). Nocturia was defined as ≥2 nocturnal voiding episodes. Logistic regression and smooth curve fitting analyzed the linear and nonlinear correlations between serum albumin and nocturia, with subgroup analysis.

RESULTS

Among 6345 participants, 1821 (28.7%) experienced nocturia. Logistic regression analysis revealed a linear negative correlation between serum albumin and nocturia risk (OR = 0.9549, 95% CI = 0.9280 ~ 0.9827, P = 0.002). Even after quartile division of serum albumin concentration, this correlation persisted within each group, and a smooth curve fitting validated the nonlinear negative correlation between the two. Subgroup analysis further demonstrated significant impacts of body mass index (BMI), alcohol consumption, and age on this association.

CONCLUSION

This cross-sectional study indicated that higher serum albumin levels were associated with a reduced risk of nocturia in U.S. adults aged 20 and older, highlighting the importance of serum albumin in the prevention and treatment of nocturia and providing clinical guidance.

Effect of Omega-3 Fatty Acids Supplementation on Homocysteine Level in Patients Undergoing Continuous Ambulatory Peritoneal Dialysis

Objective

One of the most common diseases with high morbidity and mortality rates is chronic kidney disease. Cardiovascular disease affects most patients with chronic kidney disorders, particularly patients undergoing dialysis; hence, appropriate prevention and management approaches are essential. This study aimed to evaluate the reduction of inflammatory biomarkers, especially homocysteine, by omega-3 fatty acids in peritoneal dialysis patients.

Methods

This study enrolled 60 peritoneal dialysis patients who met specified inclusion and exclusion criteria and were randomized to intervention or placebo groups. Omega-3 capsules were given at a dose of 3 g/d for 8 weeks. Inflammatory markers, including high-sensitivity C-reactive protein (hs-CRP), homocysteine, albumin, and lipid profile measured before and after the study.

Findings

Results of this trial revealed that the levels of homocysteine, hs-CRP, and albumin did not change significantly during the study. Analysis of lipid profiles before and after intervention showed omega-3 has no significant effect on the level of total cholesterol or low-density lipoprotein cholesterol; However, the level of triglyceride reduced remarkably (P = 0.002). In addition, serum levels of high-density lipoprotein cholesterol increased at the end of the study (P < 0.001).

Conclusion

Omega-3 does not seem to be able to change the inflammatory markers significantly, particularly homocysteine. More extensive trials must be conducted to better understand the impact of omega-3 on inflammatory and nutritional markers, particularly in peritoneal dialysis patients.

Improving the circulation time and renal therapeutic potency of extracellular vesicles using an endogenous ligand binding strategy

Kidney diseases are a serious health issue worldwide, and novel therapeutics are urgently needed. Extracellular vesicles (EVs) have emerged as potent drug delivery systems (DDSs), but their therapeutic potential is limited by short circulation times and insufficient renal retention. Here, we report that endogenous ligand (albumin, ALB) binding is an efficient modification strategy to improve the therapeutic potency of EV-based DDSs for kidney diseases. Surface albumin-binding peptide (ABP)-displayed EVs (ABP-EVs) were produced by transfecting parent cells with the ABP-Lamp2b fusion plasmid. Compared with unmodified EVs (NC-EVs), ABP-EVs showed increased binding to ALB in vitro and elevated circulation time and multiple organ retention in vivo after systemic (iv) injection. Moreover, ABP-EVs had higher renal retention than NC-EVs in mice with acute kidney injury through a complex mechanism involving microvascular injury and megalin-mediated endocytosis. As a result, delivery of small molecule drugs (e.g., curcumin) or proteins (e.g., hepatocyte growth factor) by ABP-EVs had superior therapeutic (e.g., anti-apoptotic, antioxidant, anti-inflammatory) effects in vitro and in vivo. This study highlights that ABP-EVs are versatile DDSs for kidney diseases and provides insights into the new strategies of engineering EVs for drug delivery.

Pathogenesis of Molar Hypomineralisation: Aged Albumin Demarcates Chalky Regions of Hypomineralised Enamel

Molar hypomineralisation (MH) is becoming globally recognised as a significant public health problem linked to childhood tooth decay. However, with causation and pathogenesis unclear after 100 years of investigation, better pathological understanding is needed if MH is to become preventable. Our studies have implicated serum albumin in an extracellular pathomechanism for chalky enamel, opposing longheld dogma about systemic injury to enamel-forming cells. Hypothesising that chalky enamel arises through developmental exposure to serum albumin, this study used biochemical approaches to characterise demarcated opacities from 6-year molars. Addressing contradictory literature, normal enamel was found to completely lack albumin subject to removal of surface contamination. Querying surface permeability, intact opacities were found to lack salivary amylase, indicating that “enamel albumin” had become entrapped before tooth eruption. Thirdly, comparative profiling of chalky and hard-white enamel supported a dose-response relationship between albumin and clinical hardness of opacities. Moreover, albumin abundance delineated chalky enamel from white transitional enamel at opacity borders. Finally, addressing the corollary that enamel albumin had been entrapped for several years, clear signs of molecular ageing (oxidative aggregation and fragmentation) were identified. By establishing aged albumin as a biomarker for chalky enamel, these findings hold methodological, clinical, and aetiological significance. Foremost, direct inhibition of enamel-crystal growth by albumin (here termed “mineralisation poisoning”) at last provides a cogent explanation for the clinical presentation of demarcated opacities. Together, these findings justify pursuit of an extracellular paradigm for the pathogenesis of MH and offer exciting new prospects for alleviating childhood tooth decay through medical prevention of MH.

Immune Dysfunction in Uremia 2020

Cardiovascular disease and infections are major causes for the high incidence of morbidity and mortality of patients with chronic kidney disease. Both complications are directly or indirectly associated with disturbed functions or altered apoptotic rates of polymorphonuclear leukocytes, monocytes, lymphocytes, and dendritic cells. Normal responses of immune cells can be reduced, leading to infectious diseases or pre-activated/primed, giving rise to inflammation and subsequently to cardiovascular disease. This review summarizes the impact of kidney dysfunction on the immune system. Renal failure results in disturbed renal metabolic activities with reduced renin, erythropoietin, and vitamin D production, which adversely affects the immune system. Decreased kidney function also leads to reduced glomerular filtration and the retention of uremic toxins. A large number of uremic toxins with detrimental effects on immune cells have been identified. Besides small water-soluble and protein-bound compounds originating from the intestinal microbiome, several molecules in the middle molecular range, e.g., immunoglobulin light chains, retinol-binding protein, the neuropeptides Met-enkephalin and neuropeptide Y, endothelin-1, and the adipokines leptin and resistin, adversely affect immune cells. Posttranslational modifications such as carbamoylation, advanced glycation products, and oxidative modifications contribute to uremic toxicity. Furthermore, high-density lipoprotein from uremic patients has an altered protein profile and thereby loses its anti-inflammatory properties.

Oral supplementation with omega-3 fatty acids and inflammation markers in patients with chronic kidney disease in hemodialysis

Chronic kidney disease (CKD) is an increasingly common public health problem that increases the risk of death because of cardiovascular complications by 2-3 times compared with the general population. This research concerns a prospective, randomized, double-blind study in patients with CKD undergoing hemodialysis. The participants were assigned to 1 of 2 groups: the study group (group A; 46 patients) received 4 capsules (2.4 g) of omega-3 fatty acids daily during the 12-week intervention, while patients in the control group (group B; 47 patients) received 4 capsules of paraffin oil. The patients' general characteristics, nutritional indicators, renal disease markers and inflammatory markers (C-reactive protein, interleukin (IL)-6, IL-10, and tumour necrosis factor alpha (TNF-α)) were evaluated. No differences were found between the general characteristics of the patients (P < 0.05), and no differences were shown in the nutritional indicators and markers of kidney disease (P < 0.05). Patients in group A showed significant decreases in levels of C-reactive protein, IL-6, TNF-α, and the IL-10/IL-6 ratio after 12 weeks of supplementation (P < 0.05). Patients in group B did not show any significant changes in concentrations of inflammatory markers during the intervention (P < 0.05). In conclusion, oral supplementation with omega-3 fatty acids produces a significant decrease in the concentrations of inflammation markers in patients with chronic kidney disease on hemodialysis. Novelty Oral supplementation with omega-3 fatty acids produced significant decreases in the concentrations of inflammation markers. This supplementation could be given to patients with uremic syndrome and coronary heart disease to reduce cardiovascular risk.

Antioxidant Effect of Sericin in Brain and Peripheral Tissues of Oxidative Stress Induced Hypercholesterolemic Rats

This study evaluated the antioxidant effect of crude sericin extract (CSE) from Antheraea assamensis in high cholesterol fed rats. Investigation was conducted by administering graded oral dose of 0.25 and 0.5 gm/kg body weight (b.w.)/day of CSE for a period of 28 days. Experiments were conducted in 30 rats and were divided into five groups: normal control, high cholesterol fed (HCF), HCF + 0.065 gm/kg b.w./day fenofibrate (FF), HCF + sericin 0.25 gm/kg b.w./day (LSD), and HCF + sericin 0.5 gm/kg b.w./day (HSD). In brain, heart, liver, serum, and kidney homogenates nitric oxide (NO), thiobarbituric acid reactive substances (TBARS), protein carbonyl content (PCC), superoxide dismutase, reduced glutathione (GSH) was measured. LSD treatment prevented the alterations in GSH and PCC levels in hypercholesterolemic (HyC) brain tissue homogenates of rats. CSE lowers the serum total cholesterol level in HyC rats by promoting fecal cholesterol (FC) excretion. CSE increases FC level by promoting inhibition of cholesterol absorption in intestine. The endogenous antioxidant reduced significantly and the oxidative stress marker TBARS level increases significantly in the peripheral tissue of HCF rats. However, the administration of LSD and HSD exhibited a good antioxidant activity by reducing the TBARS level and increasing the endogenous antioxidant in peripheral tissue. In addition, a histological examination revealed loss of normal liver and kidney architecture in cholesterol fed rats which were retained in sericin treated groups. The findings of this study suggested that CSE improves hypercholesterolemia in rats fed a HyC diet. Clinical relevance of this effect of CSE seems worthy of further studies.

Guanidinylations of albumin decreased binding capacity of hydrophobic metabolites

AIM

As post-translational modifications of proteins may have an impact on the pathogenesis of diseases such as atherosclerosis, diabetes mellitus and chronic kidney disease (CKD), post-translational modifications are currently gaining increasing interest. In this study, a comprehensive method for analysis of these post-translational modifications is established for the clinical diagnostic routine.

METHODS

Here, we analysed albumin - the most abundant plasma protein in human - isolated from patients with CKD and healthy controls by chromatographic steps and identified by MALDI mass spectrometry. Post-translational modifications of albumin were identified after digestion by analysing mass signal shifts of albumin peptides using pertinent mass databases.

RESULTS

Albumin isolated from plasma of patients with CKD but not from healthy control subjects was specifically post-translationally modified by guanidinylation of lysines at positions 249, 468, 548, 565 and 588. After identification of guanidinylations as post-translational modifications of albumin isolated from patients with CKD, these modifications were quantified by mass spectrometry demonstrating a significant increase in the corresponding mass signal intensities in patients with CKD compared to healthy controls. The relative amount of guanidinylation of lysine at position 468 in patients with CKD was determined as 63 ± 32% (N = 3). Subsequently, we characterized the pathophysiological impact of the post-translational guanidinylation on the binding capacity of albumin for representative hydrophobic metabolic waste products. In vitro guanidinylation of albumin from healthy control subjects caused a decreased binding capacity of albumin in a time-dependent manner. Binding of indoxyl sulphate (protein-bound fraction) decreased from 82 ± 1% of not post-translationally modified albumin to 56 ± 1% after in vitro guanidinylation (P < 0.01), whereas the binding of tryptophan decreased from 20 to 4%. These results are in accordance with the binding of indoxyl sulphate to albumin from healthy control subjects and patients with CKD (88 ± 3 vs. 74 ± 10, P < 0.01). Thus, in vitro post-translational guanidinylation of albumin had a direct effect on the binding capacity of hydrophobic metabolites such as indoxyl sulphate and tryptophan.

CONCLUSION

We used a mass spectrometry-based method for the characterization of post-translational modification and demonstrated the pathophysiological impact of a representative post-translational modification of plasma albumin. The data described in this study may help to elucidate the pathophysiological role of protein modifications.

Proteomics reveals plasma profiles for monitoring the toxicity caused by chromium compounds

BACKGROUND

Today, various heavy metals are widespread in the ecosystem and have become important environmental contaminants. Exposure to these hazardous metals such as chromium usually results in cytotoxicity and large-scale protein changes which reflect pathologic states.

METHODS

We used a comprehensive proteomic tool to survey changes in plasma proteins elicited by two chromium species (Cr(6+) and Cr(3+)). RT-PCR was applied to evaluate levels of cytokines associated with adverse responses. Lectin blotting was used to investigate the contents of fucosylated proteins.

RESULTS

Protein profiles revealed statistically significant changes in the intensity of 12 proteins. The network analysis implied that Cr(6+) application strongly induced the IL-6-stimulated inflammatory pathway. mRNA levels of specific cytokines were also correlated with inflammatory events. Increased IL-6 modulation of the fucosylation of haptoglobin was also identified in Cr(6+)-treated samples.

CONCLUSIONS

These results suggest that Cr(6+) may induce IL-6-mediated inflammatory responses which result in hepatic injury. This paper highlights the applications of functional proteomics of plasma profiles and fucosylated glycoproteins as a predictive tool to monitor human health in contact with chromium.

Immune dysfunction in uremia

Kidney dysfunction leads to disturbed renal metabolic activities and to impaired glomerular filtration, resulting in the retention of toxic solutes affecting all organs of the body. Cardiovascular disease (CVD) and infections are the main causes for the increased occurrence of morbidity and mortality among patients with chronic kidney disease (CKD). Both complications are directly or indirectly linked to a compromised immune defense. The specific coordinated roles of polymorphonuclear leukocytes (PMNLs), monocytes/macrophages, lymphocytes and antigen-presenting cells (APCs) in maintaining an efficient immune response are affected. Their normal response can be impaired, giving rise to infectious diseases or pre-activated/primed, leading to inflammation and consequently to CVD. Whereas the coordinated removal via apoptosis of activated immune cells is crucial for the resolution of inflammation, inappropriately high apoptotic rates lead to a diminished immune response. In uremia, the balance between pro- and anti-inflammatory and between pro- and anti-apoptotic factors is disturbed. This review summarizes the interrelated parameters interfering with the immune response in uremia, with a special focus on the non-specific immune response and the role of uremic toxins.