Ancient insights into uric acid metabolism in primates

A widely distributed gene cluster compensates for uricase loss in hominids

Approximately 15% of US adults have circulating levels of uric acid above its solubility limit, which is causally linked to the disease gout. In most mammals, uric acid elimination is facilitated by the enzyme uricase. However, human uricase is a pseudogene, having been inactivated early in hominid evolution. Though it has long been known that uric acid is eliminated in the gut, the role of the gut microbiota in hyperuricemia has not been studied. Here, we identify a widely distributed bacterial gene cluster that encodes a pathway for uric acid degradation. Stable isotope tracing demonstrates that gut bacteria metabolize uric acid to xanthine or short chain fatty acids. Ablation of the microbiota in uricase-deficient mice causes severe hyperuricemia, and anaerobe-targeted antibiotics increase the risk of gout in humans. These data reveal a role for the gut microbiota in uric acid excretion and highlight the potential for microbiome-targeted therapeutics in hyperuricemia.

The role of gut microbiota in gout: Is gut microbiota a potential target for gout treatment

Numerous studies have demonstrated that gut microbiota is essential for the host's health because it regulates the host's metabolism, endocrine, and immune systems. In recent years, increasing evidence has shown that gut microbiota plays a role in the onset and progression of gout. Changes in the composition and metabolism of the gut microbiota, result in abnormalities of uric acid degradation, increasing uric acid generation, releasing pro-inflammatory mediators, and intestinal barrier damage in developing gout. As a result, gout therapy that targets gut microbiota has drawn significant interest. This review summarized how the gut microbiota contributes to the pathophysiology of gout and how gout affects the gut microbiota. Additionally, this study explained how gut microbiota might serve as a unique index for the diagnosis of gout and how conventional gout treatment medicines interact with it. Finally, prospective therapeutic approaches focusing on gut microbiota for the prevention and treatment of gout were highlighted, which may represent a future avenue in gout treatment.

Supplementation of Lactobacillus plantarum (TCI227) Prevented Potassium-Oxonate-Induced Hyperuricemia in Rats

Hyperuricemia (HC) is one of the important risk factors for gout, arteriosclerosis, and cardiovascular disease. Animal studies have shown that Lactobacillus plantarum can improve microbiota and immune regulation, as well as inhibit uric acid production. However, it is not clear whether L. plantarum can improve HC and intestinal microbiota. We used potassium oxonate (PO) to induce HC in male SD rats and then treated them with L. plantarum TCI227 in a dose-dependent manner (HC + LD, HC + MD, HC + HD) for 4 weeks. We examined organ weight, conducted biochemical examinations of blood and urine, and analyzed the intestinal microbiota in feces through a 16s rDNA sequence analysis. In this study, TCI227 improved body weight, decreased creatinine and serum uric acid, and increased urine uric acid compared to the HC group. Furthermore, TCI227 increased short-chain fatty acids (SCFAs). In the fecal microbiota (family), TCI227 increased the level of Lactobacillaceae and then decreased the levels of Deferribacteres and Prevotellaceae compared to the HC group. Finally, in the fecal microbiota (genus), TCI227 decreased the level of Prevotella and then increased the levels of Lactobacillus and Ruminococcus compared to the HC group. This study suggested that TCI227 can improve HC and can change the composition of intestinal microbiota in PO-induced male HC SD rats.

Computational Approach for Rational Design of Fusion Uricase with PAS Sequences

Tumor lysis syndrome is a life-threatening condition for humans due to the lack of urate oxidase. In this study, several variants of PASylated uricase from the Aspergillus flavus species were analyzed computationally to find the appropriate fusions to solve short half-life and stability concern. The Ab initio method was performed using Rosetta software to structurally characterize the PAS sequences. The 3D structures of fusions were predicted for fused C- or N-terminally PAS sequences in different length to the uricase. The refinement and energy minimization steps revealed that physicochemical and conformational properties of fusions improved while the structures possessed prolonged PAS sequences. Molecular docking results showed that the highest binding affinity to uric acid belonged to uricase-PAS1-100 by the formation of six hydrogen and four non-hydrogen bonds. Altogether, the results indicated that the PASylation process would be promising upon the production of urate oxidase with improved solubility and stability.

Enhancement of Pharmaceutical Urate Oxidase Thermostability by Rational Design of De Novo Disulfide Bridge

Background and Purpose

As a therapeutic enzyme, urate oxidase is utilized in the reduction of uric acid in various conditions such as gout or tumor syndrome lysis. However, even bearing kinetical advantage over other counterparts, it suffers from structural instability most likely due to its subcellular and fungal origin.

Objectives

In this research, by using rational design and introduction of de novo disulfide bridge in urate oxidase structure, we designed and created a thermostable urate oxidase for the first time.

Materials and Methods

Utilizing site-directed mutagenesis and only with one point mutation we constructed two separate mutants: Ala6Cys and Ser282Cys which covalently linked subunits of enzyme each other. Single mutation to cysteine created three inter-chain disulfide bridges and one hydrogen bond in Ala6Cys and two disulfide bridges in Ser282Cys.

Results

Both mutants showed 10 °C increase in optimum activity compared to wild-type enzyme while the K_m values for both increased by 50% and their specific activity compromised. The thermal stability of Ser282Cys increased remarkably by comparing Ala6Cys and wild-type enzymes. Estimation of half life for wild-type enzyme demonstrated 38.5 min, while for Ala6Cys and Ser282Cys were 138 and 115 min, respectively. Interestingly, the optimal pH of both mutants was broaden from 7 to 10, which could make them candidates for industrial applications.

Conclusion

It seemed that introducing disulfide bridges resulted in local and overall rigidity by bringing two adjacent sites of enzyme together and decreasing the conformational entropy of unfolding state is responsible for the enhancement of thermostability.

Urate-induced immune programming: Consequences for gouty arthritis and hyperuricemia

Trained immunity is a process in which innate immune cells undergo functional reprogramming in response to pathogens or damage-associated molecules leading to an enhanced non-specific immune response to subsequent stimulation. While this capacity to respond more strongly to stimuli is beneficial for host defense, in some circumstances it can lead to maladaptive programming and chronic inflammation. Gout is characterized by persistent low-grade inflammation and is associated with an increased number of comorbidities. Hyperuricemia is the main risk factor for gout and is linked to the development of comorbidities. Several experimental studies have shown that urate can mechanistically alter the inflammatory capacity of myeloid cells, while observational studies have indicated an association of hyperuricemia to a wide spectrum of common adult inflammatory diseases. In this review, we argue that hyperuricemia is a main culprit in the development of the long-term systemic inflammation seen in gout. We revisit existing evidence for urate-induced transcriptional and epigenetic reprogramming that could lead to an altered functional state of circulating monocytes consisting in enhanced responsiveness and maladaptive immune responses. By discussing specific functional adaptations of monocytes and macrophages induced by soluble urate or monosodium urate crystals and their contribution to inflammation in vitro and in vivo, we further enforce that urate is a metabolite that can induce innate immune memory and we discuss future research and possible new therapeutic approaches for gout and its comorbidities.

Rate-controlled nano-layered assembly mechanism of melamine-induced melamine–uric acid stones and its inhibition and elimination methods

The formation of kidney stones induced by melamine is a rate-controlled nano-scale supramolecular layered assembly process.

The sedentary (r)evolution: Have we lost our metabolic flexibility?

During the course of evolution, up until the agricultural revolution, environmental fluctuations forced the human species to develop a flexible metabolism in order to adapt its energy needs to various climate, seasonal and vegetation conditions. Metabolic flexibility safeguarded human survival independent of food availability. In modern times, humans switched their primal lifestyle towards a constant availability of energy-dense, yet often nutrient-deficient, foods, persistent psycho-emotional stressors and a lack of exercise. As a result, humans progressively gain metabolic disorders, such as the metabolic syndrome, type 2 diabetes, non-alcoholic fatty liver disease, certain types of cancer, cardiovascular disease and Alzheimer´s disease, wherever the sedentary lifestyle spreads in the world. For more than 2.5 million years, our capability to store fat for times of food shortage was an outstanding survival advantage. Nowadays, the same survival strategy in a completely altered surrounding is responsible for a constant accumulation of body fat. In this article, we argue that the metabolic disease epidemic is largely based on a deficit in metabolic flexibility. We hypothesize that the modern energetic inflexibility, typically displayed by symptoms of neuroglycopenia, can be reversed by re-cultivating suppressed metabolic programs, which became obsolete in an affluent environment, particularly the ability to easily switch to ketone body and fat oxidation. In a simplified model, the basic metabolic programs of humans' primal hunter-gatherer lifestyle are opposed to the current sedentary lifestyle. Those metabolic programs, which are chronically neglected in modern surroundings, are identified and conclusions for the prevention of chronic metabolic diseases are drawn.

The sedentary (r)evolution: Have we lost our metabolic flexibility?

During the course of evolution, up until the agricultural revolution, environmental fluctuations forced the human species to develop a flexible metabolism in order to adapt its energy needs to various climate, seasonal and vegetation conditions. Metabolic flexibility safeguarded human survival independent of food availability. In modern times, humans switched their primal lifestyle towards a constant availability of energy-dense, yet often nutrient-deficient, foods, persistent psycho-emotional stressors and a lack of exercise. As a result, humans progressively gain metabolic disorders, such as the metabolic syndrome, type 2 diabetes, non-alcoholic fatty liver disease, certain types of cancer, cardiovascular disease and Alzheimer´s disease, wherever the sedentary lifestyle spreads in the world. For more than 2.5 million years, our capability to store fat for times of food shortage was an outstanding survival advantage. Nowadays, the same survival strategy in a completely altered surrounding is responsible for a constant accumulation of body fat. In this article, we argue that the metabolic disease epidemic is largely based on a deficit in metabolic flexibility. We hypothesize that the modern energetic inflexibility, typically displayed by symptoms of neuroglycopenia, can be reversed by re-cultivating suppressed metabolic programs, which became obsolete in an affluent environment, particularly the ability to easily switch to ketone body and fat oxidation. In a simplified model, the basic metabolic programs of humans’ primal hunter-gatherer lifestyle are opposed to the current sedentary lifestyle. Those metabolic programs, which are chronically neglected in modern surroundings, are identified and conclusions for the prevention of chronic metabolic diseases are drawn.

Physiological functions and pathogenic potential of uric acid: A review

Uric acid is synthesized mainly in the liver, intestines and the vascular endothelium as the end product of an exogenous pool of purines, and endogenously from damaged, dying and dead cells, whereby nucleic acids, adenine and guanine, are degraded into uric acid. Mentioning uric acid generates dread because it is the established etiological agent of the severe, acute and chronic inflammatory arthritis, gout and is implicated in the initiation and progress of the metabolic syndrome. Yet, uric acid is the predominant anti-oxidant molecule in plasma and is necessary and sufficient for induction of type 2 immune responses. These properties may explain its protective potential in neurological and infectious diseases, mainly schistosomiasis. The pivotal protective potential of uric acid against blood-borne pathogens and neurological and autoimmune diseases is yet to be established.

Development of Therapeutic Chimeric Uricase by Exon Replacement/Restoration and Site-Directed Mutagenesis

The activity of urate oxidase was lost during hominoid evolution, resulting in high susceptibility to hyperuricemia and gout in humans. In order to develop a more “human-like” uricase for therapeutic use, exon replacement/restoration and site-directed mutagenesis were performed to obtain porcine–human uricase with higher homology to deduced human uricase (dHU) and increased uricolytic activity. In an exon replacement study, substitution of exon 6 in wild porcine uricase (wPU) gene with corresponding exon in dhu totally abolished its activity. Substitutions of exon 5, 3, and 1–2 led to 85%, 60%, and 45% loss of activity, respectively. However, replacement of exon 4 and 7–8 did not significantly change the enzyme activity. When exon 5, 6, and 3 in dhu were replaced by their counterparts in wpu, the resulting chimera H_1-2P₃H₄P_5-6H_7-8 was active, but only about 28% of wPU. Multiple sequence alignment and homology modeling predicted that mutations of E24D and E83G in H_1-2P₃H₄P_5-6H_7-8 were favorable for further increase of its activity. After site-directed mutagenesis, H_1-2P₃H₄P_5-6H_7-8 (E24D & E83G) with increased homology (91.45%) with dHU and higher activity and catalytic efficiency than the FDA-approved porcine–baboon chimera (PBC) was obtained. It showed optimum activity at pH 8.5 and 35 °C and was stable in a pH range of 6.5–11.0 and temperature range of 20–40 °C.

DNA shuffling of uricase gene leads to a more "human like" chimeric uricase with increased uricolytic activity

Urate oxidase (Uox) is the enzyme involved in purine metabolism. Pseudogenization of Uox gene is the underlying mechanism of hyperuricemia and gout in human. Although Uox from various microorganisms has been used in clinical practice for many years, its application is limited by potential immunogenicity. In order to develop a more "human like" uricase, DNA shuffling was used to create chimeric uricase with both improved enzymatic activity and increased homology with deduced human uricase (dHU) gene. By using wild porcine uricase (wPU) gene and dhu as parental genes, a diverse chimeric library was generated. After preliminary screening by a "homebrew" high throughput protocol, approximately 100 chimeras with relatively high enzymatic activity were obtained. By further activity comparison of the purified enzymes, chimera-62 with increase in both activity and homology with dHU compared with wPU was selected. Its Km and catalytic efficiency were determined as 9.43±0.04μM and 2.67s(-1)μM(-1) respectively. There were 33 amino acid substitutions in chimera-62 when compared with dHU and 5 substitutions when compared with wPU. By homology modeling and 3-D structure analysis, it was speculated that mutations G248S and L266F contributed to the increased activity of chimera-62 by increasing the stability of α-helix and surface polarity respectively.

ABCG2: the molecular mechanisms of urate secretion and gout

The human propensity for high levels of serum uric acid (SUA) is a trait that has defied explanation. Is it beneficial? Is it pathogenic? Its role in the human diseases like gout and kidney stones was discovered over a century ago [Richette P, Bardin T. Lancet 375: 318-328, 2010; Rivard C, Thomas J, Lanaspa MA, Johnson RJ. Rheumatology (Oxford) 52: 421-426, 2013], but today emerging new genetic and epidemiological techniques have revived an age-old debate over whether high uric acid levels (hyperuricemia) independently increase risk for diseases like hypertension and chronic kidney disease [Feig DI. J Clin Hypertens (Greenwich) 14: 346-352, 2012; Feig DI, Madero M, Jalal DI, Sanchez-Lozada LG, Johnson RJ. J Pediatr 162: 896-902, 2013; Feig DI, Soletsky B, Johnson RJ. JAMA 300: 924-932, 2008; Wang J, Qin T, Chen J, Li Y, Wang L, Huang H, Li J. PLoS One 9: e114259, 2014; Zhu P, Liu Y, Han L, Xu G, Ran JM. PLoS One 9: e100801, 2014]. Part of the mystery of the role uric acid plays in human health stems from our lack of understanding of how humans regulate uric acid homeostasis, an understanding that could shed light on the historic role of uric acid in human adaptation and its present role in human pathogenesis. This review will highlight the recent work to identify the first important human uric acid secretory transporter, ABCG2, and the identification of a common causal ABCG2 variant, Q141K, for hyperuricemia and gout.