Compounds protective against renal tubular necrosis induced by D-serine and D-2,3-diaminopropionic acid in the rat

Rv0547c, a functional oxidoreductase, supports Mycobacterium tuberculosis persistence by reprogramming host mitochondrial fatty acid metabolism

Mycobacterium tuberculosis (Mtb) successfully thrives in the host by adjusting its metabolism and manipulating the host environment. In this study, we investigated the role of Rv0547c, a protein that carries mitochondria-targeting sequence (MTS), in mycobacterial persistence. We show that Rv0547c is a functional oxidoreductase that targets host-cell mitochondria. Interestingly, the localization of Rv0547c to mitochondria was independent of the predicted MTS but depended on specific arginine residues at the N- and C-terminals. As compared to the mitochondria-localization defective mutant, Rv0547c-2SDM, wild-type Rv0547c increased mitochondrial membrane fluidity and spare respiratory capacity. To comprehend the possible reason, comparative lipidomics was performed that revealed a reduced variability of long-chain and very long-chain fatty acids as well as altered levels of phosphatidylcholine and phosphatidylinositol class of lipids upon expression of Rv0547c, explaining the increased membrane fluidity. Additionally, the over representation of propionate metabolism and β-oxidation intermediates in Rv0547c-targeted mitochondrial fractions indicated altered fatty acid metabolism, which corroborated with changes in oxygen consumption rate (OCR) upon etomoxir treatment in HEK293T cells transiently expressing Rv0547c, resulting in enhanced mitochondrial fatty acid oxidation capacity. Furthermore, Mycobacterium smegmatis over expressing Rv0547c showed increased persistence during infection of THP-1 macrophages, which correlated with its increased expression in Mtb during oxidative and nutrient starvation stresses. This study identified for the first time an Mtb protein that alters mitochondrial metabolism and aids in survival in host macrophages by altering fatty acid metabolism to its benefit and, at the same time increases mitochondrial spare respiratory capacity to mitigate infection stresses and maintain cell viability.

D-Serine as a sensor and effector of the kidney

D-Serine, a rare enantiomer of serine, is a biomarker of kidney disease and function. The level of D-serine in the human body is precisely regulated through the urinary clearance of the kidney, and its clearance serves as a new measure of glomerular filtration rate with a lower bias than creatinine clearance. D-Serine also has a direct effect on the kidneys and mediates the cellular proliferation of tubular cells via mTOR signaling and induces kidney remodeling as a compensatory reaction to the loss of kidney mass. In living kidney donors, the removal of the kidney results in an increase in blood D-serine level, which in turn accelerates kidney remodeling and augments kidney clearance, thus reducing blood levels of D-serine. This feedback system strictly controls D-serine levels in the body. The function of D-serine as a biomarker and modulator of kidney function will be the basis of precision medicine for kidney diseases.

An Untargeted Metabolomics Approach on Carfilzomib-Induced Nephrotoxicity

BACKGROUND

Carfilzomib (Cfz) is an anti-cancer drug related to cardiorenal adverse events, with cardiovascular and renal complications limiting its clinical use. Despite the important progress concerning the discovery of the underlying causes of Cfz-induced nephrotoxicity, the molecular/biochemical background is still not well clarified. Furthermore, the number of metabolomics-based studies concerning Cfz-induced nephrotoxicity is limited.

METHODS

A metabolomics UPLC-HRMS-DIA methodology was applied to three bio-sample types i.e., plasma, kidney, and urine, obtained from two groups of mice, namely (i) Cfz (8 mg Cfz/ kg) and (ii) Control (0.9% NaCl) (n = 6 per group). Statistical analysis, involving univariate and multivariate tools, was applied for biomarker detection. Furthermore, a sub-study was developed, aiming to estimate metabolites' correlation among bio-samples, and to enlighten potential mechanisms.

RESULTS

Cfz mostly affects the kidneys and urine metabolome. Fifty-four statistically important metabolites were discovered, and some of them have already been related to renal diseases. Furthermore, the correlations between bio-samples revealed patterns of metabolome alterations due to Cfz.

CONCLUSIONS

Cfz causes metabolite retention in kidney and dysregulates (up and down) several metabolites associated with the occurrence of inflammation and oxidative stress.

D-Amino acids and kidney diseases

d-Amino acids are the recently detected enantiomers of l-amino acids. Accumulating evidence points their potential in solving the long-standing critical problems associated with the management of both chronic and acute kidney diseases. This includes estimating kidney function, early diagnosis and prognosis of chronic kidney disease, and disease monitoring. Among the d-amino acids, d-serine levels in the blood are strongly correlated with the glomerular filtration rate and are useful for estimating the function of the kidney. Urinary d-serine also reflects other conditions. The kidney proximal tubule reabsorbs serine with chiral-selectivity, with d-serine being reabsorbed much less efficiently than l-serine, and urinary excretion of d-serine is sensitive to the presence of kidney diseases. Therefore, assessing the intra-body dynamics of d-serine by measuring its level in blood and urinary excretion can be used to detect kidney diseases and assess pathophysiology. This new concept, the intra-body dynamics of d-serine, can be useful in the comprehensive management of kidney disease.

6 Final Report on the Safety Assessment of Aminomethylpropanol and Aminomethylpropanediol

AMP and AMPD are substituted aliphatic alcohols. AMP is used in cosmetic products at concentrations up to 10%, AMPD is used at concentrations up to 5%. AMP and AMPD when buffered, and orally administered, are practically nontoxic to rats and mice.

In primary irritation studies, AMP and formulations containing AMP were, at most, minimally irritating to abraded and nonabraded rabbit skin. Cosmetic formulations containing AMPD were only minimally irritating to rabbit skin. AMP was not an intradermal sensitizer in guinea pigs. Cosmetic formulations containing AMPD and/or AMP were minimal to moderate ocular irritants.

AMP and AMPD were nonmutagenic, both with and without metabolic activation, in Salmonella typhimurium strains.

In clinical studies, AMP was neither a primary dermal irritant nor a contact sensitizer. AMPD was neither a primary irritant, fatiguing agent, nor sensitizer when tested in humans.

AMP and AMPD are highly alkaline in pure form, they are buffered in cosmetic formulations, and, therefore, the adverse reactions seen with the undiluted chemical would not be expected with the cosmetic product. The highest level of both AMP and AMPD for which test data were available was 1.0%, therefore the safe use of these two compounds should be limited to this test value. Neither ingredient should be used in cosmetic products containing nitrosating agents.

Chiral amino acid metabolomics for novel biomarker screening in the prognosis of chronic kidney disease

D-Amino acids, the enantiomers of L-amino acids, are increasingly recognized as novel biomarkers. Although the amounts of D-amino acids are usually very trace in human, some of them have sporadically been detected in blood from patients with kidney diseases. This study examined whether multiple chiral amino acids would be associated with kidney functions, comorbidities, and prognosis of chronic kidney disease (CKD) by enantioselective analyses of all chiral amino acids with a micro-two-dimensional high-performance liquid chromatograph (2D-HPLC)-based analytical platform. 16 out of 21 D-amino acids were detected in plasma from 108 CKD patients in a longitudinal cohort. The levels of D-Ser, D-Pro, and D-Asn were strongly associated with kidney function (estimated glomerular filtration ratio), the levels of D-Ala and D-Pro were associated with age, and the level of D-Asp and D-Pro were associated with the presence of diabetes mellitus. D-Ser and D-Asn were significantly associated with the progression of CKD in mutually-adjusted Cox regression analyses; the risk of composite end point (developing to ESKD or death before ESKD) was elevated from 2.7- to 3.8-fold in those with higher levels of plasma D-Ser and D-Asn. These findings identified chiral amino acids as potential biomarkers in kidney diseases.

Ischemic acute kidney injury perturbs homeostasis of serine enantiomers in the body fluid in mice: early detection of renal dysfunction using the ratio of serine enantiomers

The imbalance of blood and urine amino acids in renal failure has been studied mostly without chiral separation. Although a few reports have shown the presence of D-serine, an enantiomer of L-serine, in the serum of patients with severe renal failure, it has remained uncertain how serine enantiomers are deranged in the development of renal failure. In the present study, we have monitored serine enantiomers using a two-dimensional HPLC system in the serum and urine of mice after renal ischemia-reperfusion injury (IRI), known as a mouse model of acute kidney injury. In the serum, the level of D-serine gradually increased after renal IRI in parallel with that of creatinine, whereas the L-serine level decreased sharply in the early phase after IRI. The increase of D-serine was suppressed in part by genetic inactivation of a D-serine-degrading enzyme, D-amino acid oxidase (DAO), but not by disruption of its synthetic enzyme, serine racemase, in mice. Renal DAO activity was detected exclusively in proximal tubules, and IRI reduced the number of DAO-positive tubules. On the other hand, in the urine, D-serine was excreted at a rate nearly triple that of L-serine in mice with sham operations, indicating that little D-serine was reabsorbed while most L-serine was reabsorbed in physiological conditions. IRI significantly reduced the ratio of urinary D−/L-serine from 2.82±0.18 to 1.10±0.26 in the early phase and kept the ratio lower than 0.5 thereafter. The urinary D−/L-serine ratio can detect renal ischemia earlier than kidney injury molecule-1 (KIM-1) or neutrophil gelatinase-associated lipocalin (NGAL) in the urine, and more sensitively than creatinine, cystatin C, or the ratio of D−/L-serine in the serum. Our findings provide a novel understanding of the imbalance of amino acids in renal failure and offer a potential new biomarker for an early detection of acute kidney injury.

The role of toxicoproteomics in assessing organ specific toxicity

Aims of this chapter on the role of toxicoproteomics in assessing organ-specific toxicity are to define the field of toxicoproteomics, describe its development among global technologies, and show potential uses in experimental toxicological research, preclinical testing and mechanistic biological research. Disciplines within proteomics deployed in preclinical research are described as Tier I analysis, involving global protein mapping and protein profiling for differential expression, and Tier II proteomic analysis, including global methods for description of function, structure, interactions and post-translational modification of proteins. Proteomic platforms used in toxicoproteomics research are briefly reviewed. Preclinical toxicoproteomic studies with model liver and kidney toxicants are critically assessed for their contributions toward understanding pathophysiology and in biomarker discovery. Toxicoproteomics research conducted in other organs and tissues are briefly discussed as well. The final section suggests several key developments involving new approaches and research focus areas for the field of toxicoproteomics as a new tool for toxicological pathology.

Why is d-serine nephrotoxic and α-aminoisobutyric acid protective?

d-Serine selectively causes necrosis of S3 segments of proximal tubules in rats. This leads to aminoaciduria and glucosuria. Coinjection of the nonmetabolizable amino acid α-aminoisobutyric acid (AIB) prevents the tubulopathy. d-serine is selectively reabsorbed in S3, thereby gaining access to peroxisomal d-amino acid oxidase (d-AAO). d-AAO-mediated metabolism produces reactive oxygen species. We determined the fractional excretion of amino acids and glucose in rats after intraperitoneal injection of d-serine alone or together with reduced glutathione (GSH) or AIB. Both compounds prevented the hyperaminoaciduria. We measured GSH concentrations in renal tissue before (control) and after d-serine injection and found that GSH levels decreased to ∼30% of control. This decrease was prevented when equimolar GSH was coinjected with d-serine. To find out why AIB protected the tubule from d-serine toxicity, we microinfused d-[14C]serine or [14C]AIB (0.36 mmol/l) together with [3H]inulin in late proximal tubules in vivo and measured the radioactivity in the final urine. Fractional reabsorption of d-[14C]serine and [14C]AIB amounted to 55 and 70%, respectively, and 80 mmol/l of AIB or d-serine mutually prevented reabsorption to a great extent. d-AAO activity measured in vitro (using d-serine as substrate) was not influenced by a 10-fold higher AIB concentration. We conclude from these results that 1) d-AAO-mediated d-serine metabolism lowers renal GSH concentrations and thereby provokes tubular damage because reduction of reactive oxygen species by GSH is diminished and 2) AIB prevents d-serine-induced tubulopathy by inhibition of d-serine uptake in S3 segments rather than by interfering with intracellular d-AAO-mediated d-serine metabolism.

A potential biomarker of kidney damage identified by proteomics: preliminary findings

4-Aminophenol (4-AP) and D-serine are established rodent nephrotoxins that selectively damage renal proximal tubules. In an attempt to understand the mechanism of action of these toxicants in greater detail, a high throughput proteomics approach was used to profile protein changes in the plasma of animals treated with these compounds. Male Fischer 344 and Alderley Park rats were treated with increasing doses of 4-AP or D-serine and plasma samples were collected over time. Control groups received either saline or the non-toxic enantiomer, L-serine. Using high throughput two-dimensional gel analysis, a number of plasma proteins showing dose- and time-dependent regulation were identified. One toxicity-associated plasma protein was identified as the cellular enzyme fumarylacetoacetate hydrolase (FAH), which is known to be required for tyrosine metabolism. The FAH gene is mutated in the human genetic disorder type I tyrosinaemia, which is associated with liver and kidney abnormalities and neurological disorders. FAH was elevated in the plasma of animals treated with 4-AP and D-serine at early time points and returned to baseline levels after 3 weeks. The protein was not elevated in the plasma of control animals or those treated with L-serine. The presence of FAH in plasma is intriguing as it is normally a cellular enzyme with no known function in plasma. It is possible that 4-AP and D-serine may work through a previously unknown mechanism in the kidney via regulation of tyrosine metabolism or FAH activity. Therefore, FAH may function in a fashion analogous to the aspartate aminotransferase (AST) and alanine aminotransferase (ALT) enzymes that are used to measure liver injury. The link between kidney toxicants and inherited tyrosinaemia also raises the possibility that FAH may be a marker of kidney toxicity in humans. These observations highlight the value of proteomics in identifying new biomarkers and providing new unprecedented insights into complex biological mechanisms.

Role of haematological, pulmonary and renal complications in the long-term prognosis of patients with lysinuric protein intolerance

Three patients with lysinuric protein intolerance are reported. The first patient displayed severe haemolytic anaemia, bone marrow erythroblastophagocytosis, renal tubular disease and interstitial lung disease. Despite treatment with citrulline and low-protein diet, this child died at the age of 18 months. The second patient is now 24 years old and has chronic interstitial lung disease and focal renal glomerulosclerosis. The third patient, now 5 years old, has severe chronic interstitial lung disease. A 6-month treatment with prednisone was ineffective in the second and third patients.

Potentiation of ischemic renal injury by amino acid infusion

The purpose of this study was to determine whether amino acid hyperalimentation sensitizes the kidney to ischemic renal injury. Sprague-Dawley rats were infused with a control infusate or control infusate plus 15 essential and nonessential amino acids (FreAmine III, 2 mg of amino acids/kg/min). After 1 hr, bilateral renal ischemia was induced (15 min pedicle cross clamp). GFR, urine flow, and renal blood flow (RBF) were measured before and for 0 to 2 hr postischemia. None of these parameters were statistically different between the two groups of rats prior to renal ischemia. However, the decrease in GFR following renal ischemia was twice as great in the amino acid versus the nonamino acid treatment group (decreases 73 +/- 4% vs. decreases 36 +/- 4%, respectively; P less than 0.001). The postischemia urine flow rate was also significantly less (P less than 0.01) with amino acid treatment. RBF did not differ between the two groups. Renal histology confirmed greater tubular injury with amino acid treatment (P less than 0.001). In conclusion, infusion of therapeutic doses of amino acids can exacerbate early functional and histologic parameters of ischemic renal injury and thus, may sensitize the kidney to ischemic acute renal failure.