BMS 150 Crystal Arthropathies PDF

PAT3.04 – Crystal Arthropathies Nucleotide metabolism Crystal Arthropathies BMS 150 Week 5 Overview Nucleotide metabolism Crystal Arthropathies Gout Pseudogout Pharmacologic agents for Gout Learning Objectives List and differentiate the general structures (ie number of rings) of purines vs pyrimidin...

PAT3.04 – Crystal Arthropathies Nucleotide metabolism Crystal Arthropathies BMS 150 Week 5 Overview Nucleotide metabolism Crystal Arthropathies Gout Pseudogout Pharmacologic agents for Gout Learning Objectives List and differentiate the general structures (ie number of rings) of purines vs pyrimidines, including whether they are found in DNA and/or RNA Differentiate the names and structures of nucleosides vs nucleotides Describe the purine (salvage and de novo) and pyrimidine synthesis pathways, including the relevant substrates, enzymes, and products (outlined in the slides) Outline the overall process, relevant intermediates and products of nucleotide catabolism (outlined in the slides) Relate the pathophysiology of Lesch-Nyhan Syndrome to purine synthesis Learning Objectives Discuss the pathophysiology, epidemiology, clinical features, diagnosis, prognosis and complication of the following diseases: Gout Pseudogout Discuss the mechanism of action, therapeutic use, and selected adverse effects of the following anti-gout agents: colchicine, allopurinol, uricosurics (ie Probenecid) Compare the clinical presentations of the arthritides in terms of: Joint distribution, symmetricity Presence of extra-articular features and length of morning stiffness Time course of presentation Review Base ▪ N-containing single (pyrimidine) or double (purine) ring structure ▪ DNA & RNA: A & G (purines), C (pyrimidine) DNA only: T (pyrim) ▪ RNA only: U (pyrim) Adenine Sugar ▪ 5-C ribose (RNA) or deoxyribose (DNA) Nucleoside ▪ Sugar + base Adenosine Pi Nucleotide ▪ Nucleoside + 1-3 phosphates Adenosine triphosphate Nucleotide Bases Bases to know (nucleoside names in brackets) (cytidine) (thymidine) Note “ine” (DNA bases) to “dine” endings (nucleosides) Uracil (in RNA) (uridine) (adenosine) xanthine (xanthosine) (guanosine) hypoxanthine (inosine) Note “ine” (bases) to “sine” endings (nucleosides) Purine Nucleotide Biosynthesis Phosphoribosyl pyrophosphate From diet, cell turnover Purines – De novo synthesis Glutamine is used to transfer an N to PRPP ▪ Results in a phosphoribose (sugar+P) with an added N ▪ Still need a base to make a nucleotide ▪ Base (2 rings) is built on this N Other amino acids, CO2 and folate (?) coenzymes supply the C, H, O and N ▪ The nucleotide product is inosine monophosphate (IMP) What, therefore, is the purine base that was made? Glutamine NH2 N PRPP IMP Purines – De novo synthesis IMP can then be used to make AMP or GMP ▪ These pathways also use: ▪ GTP to make AMP ▪ ATP make GMP This allows for reciprocal control: when ATP is high you make GMP, when GTP is high is make AMP ▪ Why do you think is type of control is useful? Purine – Salvage pathway Important to have, as de novo uses lots of energy Uses hypoxanthine, guanine, and adenine bases that already exist ▪ Where do they come from? ▪ What do you still need to add to get a nucleotide? Purine – Salvage pathway Enzymes: ▪ Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) Catalyzes the addition of phosphoribose (sugar+P) from PRPP to: ▪ Hypoxanthine to make IMP ▪ Guanine to make GMP ▪ Adenine phosphoribosyltransferase (APRT) Catalyzes the addition of phosphoribose (sugar+P) from PRPP to: ▪ Adenine to make AMP Purines: Salvage + De Novo Glutamine, other aa's, CO2, folate Pyrimidine Nucleotide Synthesis De novo pathway, involves making an intermediate pyrimidine ring first, then attaching a ribose-5-P (via PRPP) ▪ Opposite to purines, where the ring is constructed directly on the ribose-5-P Substrates for ring are: ▪ Carbamoyl phosphate (made from glutamine, ATP, CO2) What other use do you know for carbamoyl phosphate? ▪ Aspartate Overview Glutamine, ATP, HCO3Carbamoyl Phosphate Aspartate Pyrimidine ring PRPP (supplies phosphoribose) Nucleotide intermediate CTP UMP dTMP Pyrmidine Nucleotide Synthesis To make CTP: ▪ UMP is phosphorylated via to make UTP ▪ UTP is aminated to make CTP UTP kinases Glutamine supplies the N To make dTMP (what does “d” mean?): CTP ▪ UMP is first phosphorylated (kinase) to make UDP, then converted to dUMP ▪ dUMP is methylated to dTMP using a folate coenzyme H3C dUMP dTMP Nucleotides Catabolism and clinical correlations Dr. Heisel BMS150 General Nucleotidases remove P’s from nucleotides to release nucleosides ▪ Sugar removed to release bases Pyrimidine bases degraded: ▪ Cytosine to uracil and ultimately alanine ▪ FYI: Thymine to aminoisobutyrate Purine bases degraded: ▪ First to xanthine, then uric acid Uric acid is eventually excreted in urine Elevated levels can lead to hyperuricemia and gout ▪ Conversion of hypoxanthine to xanthine, and xanthine to uric acid, uses the enzyme xanthine oxidase Gout Can be due to underexcretion (most common) or overproduction (less common) of uric acid → hyperuricemia Hyperuricemia can lead to gout ▪ Deposition of monosodium urate crystals in the joints → immune cells mount an inflammatory response to crystals Known as gout (gouty arthritis) ▪ Nodular masses of monosodium urate crystals (tophi) may be deposited in soft tissues Known as chronic tophaceous gout ▪ Uric acid stones can form in the kidneys (urolithiasis) Gout - intro Humans lack uricase, the enzyme responsible for the degradation of uric acid in other mammals ▪ Uric acid is also highly reabsorbed in the urine ▪ Major modifiable risk factors include diets rich in alcohol (beer has quite a few purines) and meat (especially organ meats), asparagus Non-modifiable include male sex (much more common in guys) and decreased renal excretion Gout = joint inflammation due to deposition of urate crystals Gout – Epidemiology & Etiology Epidemiology: 10% - 20% of the population of the Western hemisphere has hyperuricemia, but not all develop gout ▪ 1 – 4% of the general population develop gout Etiology Increased uric acid production: ▪ Enzyme defects in degradation of uric acid ▪ Rapidly-dividing cancers – i.e. leukemia Decreased uric acid excretion (in the kidneys) ▪ Idiopathic ▪ Chronic kidney disease FYI: Primary gout → gout due to diet, idiopathic overproduction or under-secretion of uric acid Secondary gout → hyperuricemia is due to an identified disorder Gout – Pathophysiology: Acute Monosodium urate crystal precipitation results in acute gouty arthritis ▪ Local anatomical factors that increase the likelihood of arthritis include: temperature, pH, trauma, joint hydration Urate crystals are phagocytosed by macrophages, activating them ▪ They then release chemokines that attract neutrophils into the joint, found within the synovial fluid Neutrophils mediate joint inflammation Gout – Pathophysiology: Acute Complement activation via the alternative pathway also contributes to neutrophil recruitment. Gout – Pathophysiology: Acute Phagocytosis by macrophages results in activation of the inflammasome ▪ Secretion of IL-1 ▪ Further promotes accumulation of neutrophils and macrophages within the joint Release cytokines, free radicals, proteases, & arachidonic acid metabolites ▪ This is a vicious cycle! Gout – Pathophysiology: Acute Phagocytosed crystals will induce rupture of phagolysosomes and lysis of neutrophils. ▪ Futher release of proteases and inflammatory mediators Eventually (within days to weeks) there will be spontaneous remission Gout – Pathophysiology: Chronic After the first attack, people enter an inter-critical phase with a varying number of acute attacks ▪ Many people will have attacks every few months Chronic gout leads to chronic arthritis with joint erosion, chronic inflammation, development of pannus, and development of tophi ▪ Urate crystals encrust the articular surface of the joint forming deposits in the synovium ▪ Synovium becomes hyperplastic, fibrotic, and thickened with inflammatory cells (ie. pannus formation) ▪ Destruction of underlying cartilage leads to bone erosion ▪ In severe cases a fibrous or bony ankylosis can form, resulting in loss of joint function. Gout – Pathophysiology: Chronic Tophi – pathognomonic hallmark of gout Large, inflammatory bodies that surround areas of crystal deposition form foreign-body giant cells Consist of macrophages and lymphocytes Occur in articular cartilage, ligaments, tendons, and bursae Can invade joint and surrounding soft tissues or kidneys Earlobes, fingertips Presence of urate crystals or tophi in kidneys can result in renal complications (urate nephropathy) Gout – Clinical Findings Clinical findings - acute: ▪ 90% of affected individuals experience acute attacks in the following locations (in descending order of frequency): 1st metatarsal-phalangeal joint, insteps, ankles, heels Knees, wrists, elbows Fingers Lower limbs are more often affected than upper ▪ Excruciatingly painful, inflamed joints (redness, swelling) characterize acute gout attacks Untreated, acute gouty arthritis may last for hours to weeks Gout – Clinical Findings Clinical findings - Chronic ▪ In the absence of appropriate therapy, the attacks recur at shorter intervals and frequently become polyarticular ▪ Eventually, over the span of years, disabling chronic tophaceous gout develops Average of 12 years between the initial acute attack and the appearance of chronic tophaceous arthritis Lesch-Nyhan Syndrome Can lead to hyperuricemia ▪ Deficiency of HGPRT (what does this enzyme do?) Leads to accumulation of hypoxanthine and guanine, which break down into ? PRPP also accumulates and stimulates production of purine nucleotides, which ultimately break down into ? ▪ Hyperuricemia frequently results in urolithiasis and gouty arthritis ▪ Severe neurological problems Calcium pyrophosphate crystal deposition disease (CPPD) – Epidemiology & Etiology Also known as pseudogout Epidemiology: ▪ Common, prevalence increases with age (reported to be present in 30 – 60% in those older than 85) Etiology: Most cases are sporadic ▪ Some have a genetic component (autosomal dominant) ▪ Can be caused by hyperparathyroidism, hemochromatosis, diabetes, hypothyroidism ▪ Some medications may trigger pseudogout – this is poorly-defined, though Calcium pyrophosphate crystal deposition disease (CPPD) - Pathology Pathology: ▪ Crystals deposit in matrix of menisci, connective tissue of joint ▪ Rupture, eliciting inflammation as macrophages phagocytose the crystals ▪ Recruit neutrophils, which are thought to mediate inflammatory damage Calcium pyrophosphate crystal deposition disease (CPPD) – Clinical Features Clinical presentation: ▪ Can be asymptomatic – can mimic osteoarthritis or rheumatoid arthritis ▪ Asymmetric, can be monoarticular or polyarticular ▪ Commonly affects knees, less common sites are wrists, shoulders, elbows, ankles ▪ Eventually 50% have significant joint damage (affects mobility) Treatment ▪ No therapy is effective in preventing damage, symptomatic treatment Synovial Fluid Analysis Why is it done? ▪ It is not always easy to distinguish between septic arthritis, gout, pseudogout, hemarthroses and rheumatic joint diseases Septic arthritis must be managed urgently Hemarthrosis and gout should also be managed (semiurgently) ▪ It’s a good test at distinguishing between an acute flare of gout or pseudogout and septic arthritis Poorer sensitivity and specificity when it’s more difficult to visualize crystals (between flares) ▪ For an acutely swollen, painful joint, it can change management Synovial Fluid Analysis When is it done? ▪ Suspicion of an infectious arthritis, flare of crystal arthritis, or hemarthrosis Monoarthritis (with or without a prior history of arthritis of other joints) trauma to a joint with effusion You analyze the three C’s: ▪ Crystals – seen under microscopy with gout and pseudogout ▪ Cells – red blood cells? Leukocytes (neutrophils or lymphocytes) ▪ Culture – any microorganisms growing in there? (takes some time) Synovial fluid analysis: crystal Monosodium urate crystals Calcium pyrophosphate crystals Synovial Fluid Analysis Disorder Cells Crystals Culture Normal < 200/ul (low) Negative Negative Gout > 2000/uL (high, but not as high as septic) Birefringent, needleshaped Negative Pseudogout > 2000/uL (high, but not as high as septic) Non-birefringent, cuboidal Negative Septic Arthritis > 50,000/uL (very high) Negative Positive Hemarthrosis Lots of RBCs Negative Negative Inflammatory Arthritis > 2000/uL (high) Negative Negative Osteoarthritis < 2000/uL (medium) Negative Negative Anti-gout agents Possible therapeutics options include: ▪ Target the inflammation General: Corticosteriods (previous lecture) Specific to gout: Colchicine ▪ Analgesics NSAIDs (ex aspirin) (previous lecture) ▪ Most common treatment ▪ Decrease uric acid production Allopurinol ▪ Increase uric acid excretion Uricosurics (probenecid and sulfinpyrazone) Colchine Mechanism of action ▪ Binds tubulin and prevents microtubule polymerization How does effect inflammation? What other condition do you think it was considered as a treatment for? ▪ Found to be too toxic ▪ Prophylactically, can reduce frequency of attacks FYI: : 0.5mg/day, 3-4 days per week ▪ Acutely, can terminate an attack if taken at first sign of inflammation FYI: 1-1.2 mg every hour until attack abates or diarrhea occurs Colchine Adverse effects ▪ Most serious is bone marrow depression Why would it potentially cause this? Requires patient blood count monitoring Requires monitoring for less serious adverse effects ▪ Ex nausea, vomiting, abdominal pain, diarrhea If appear, drug should be discontinued for at least 3 days to prevent cumulative toxicity leading to more serious effects Allopurinol and Uricosurics Allopurinol ▪ Competitive inhibitor of xanthine oxidase (?) ▪ Do you think it is useful prophylactically, acutely, or both? ▪ Can precipitate an attack of gout at the beginning of therapy – why? As uric acid concentrations go down, crystals start to dissolve and the immune system responds ▪ Typically give aspirin at beginning of allopurinol therapy to reduce pain Uricosurics ▪ Block tubular reabsorption of uric acid, increasing excretion ▪ Do you think it is useful prophylactically, acutely, or both? ▪ Do you think it can precipitate an attack of gout at the beginning of therapy?