Production deficiencies/errors

As is true of most inborn errors, the signs and symptoms of porphyria result from either a deficiency of metabohc products beyond the enzymatic block or from an accumulation of metabolites behind the block. 

Still, some members of the lay public are clearly skeptical of science and scientists, as indicated by the view of the profession presented on the cover of a national magazine in Figure 6.110 Although we may be assured that scientists as a group are no more deficient in morals than, say, cartoonists, it is important to understand the basis of public perceptions and to examine the practical implications for laboratory management. Industrial products are very widely distributed and many are used intimately. There are real consequences that can arise from a serious error in manufacture or design, as illustrated by the case of L-tryptophan. 

The resulting dependences of [Th/Eu] on stellar age are shown in Fig. 10.5, together with a selection of observational data from del Peloso et al. for disk stars Westin et al. (2000) for two of the r-process enriched ultra-metal-poor (UMP) halo stars and Cowan et al. (2002) for a third one. The range among disk stars is little more than can be expected from uncertainties in the determination, while the UMP stars show more or less the expected deficiency. For BD +17 0 3248, Cowan et al. used theoretical production ratios for Th relative to Eu, Ir and Pt, based on certain nuclear models, to deduce a Galactic-model-independent age of 13.8 4 Gyr, which happens to fit our two production-ratio-independent model curves simple inflow and modFowler T = 15 quite nicely, but the error bars are large so that what we have is more a test of consistency than an independent chronometer. 

The findings demonstrated that DRD is caused by a partial BH4 deficiency in the brain. In general, disorders caused by an inborn error of metabobsm show recessive inheritance, as half of the enzyme activity is usually sufficient enough to maintain homeostasis in vivo. To the contrary, DRD is a dominant disorder with low penetrance, even though the causative gene for DRD is that for an enzyme, GCH. The marked decrease (to approximately 20% of controls) in the neopterin content in the CSF (cerebrospinal fluid) from DRD patients suggests that GCH activity in the brain of DRD patients is also about 20% of that for normal individuals. Because neopterin is a metabolite of dihy-droneopterin triphosphate, the product of GCH, the neopterin content in the CSF is thought to reflect the GCH activity in the brain. 

Traditional batch processing involves periodic monitoring of quality. A pill production line, for example, may be monitored by examining every 10 thousandth pill for integrity, coating, and stamp. If a given pill is found to be deficient, all pills produced in that batch of 10,000 would be recycled, discarded, or reexamined. The process can potentially add unnecessary expense to the production process and can lead to possible inappropriate release from quarantine (pills are stored until passed, creating possible human error in premature shipment). 

Inborn errors of metabolism are normally associated with a deficiency or absence of an enzyme. Can excessive production of an enzyme also result in an inborn error of metabolism ... 

A deficient design of a catalyst pellet for a single reaction leads to a poor utilization of the often expensive catalyst mass. Fortunately, we can usually adjust some operating conditions, such as the temperature or residence time, or install additional catalyst material to compensate for a design error. This section discusses the influence of diffusion limitations on the yield of the desired product in a multipath reaction. Here, when the diffusion intrusions are not properly accounted for, it is often impossible to counterbalance the impact of the design error by a change in the operating conditions. 

The most recent application of RPLC to the analysis of enzymes has been reported by Halfpenny and Brown (HI). An assay for purine nucleoside phosphorylase, a key mediator in the purine salvage pathway, has been developed and optimal conditions for the analysis determined. Figure 20 illustrates the simultaneous separation of the substrate, inosine, and products, uric acid and hypoxanthine. In another analysis. Halfpenny and Brown (H2) developed an assay for hypoxanthine-guanine phos-phoribosyltransferase. Deficiency of this enzyme has been associated with Lesch-Nyhan syndrome as well as primary gout. The activity of the enzyme is determined by measurement of the decrease of the substrate, hypoxanthine, and increase in the product, inosine-5 -monophosphoric acid. A major advantage of using HPLC for enzyme assays is that the simultaneous measurement of both substrate and product reduces the error due to interference from competing enzymes. 

Deficient application, operational error, or system malfunction could potentially affect the manufacture of all the products using the MRP II system. A single medium-sized secondary manufacturing site may have an associated annual drug sales revenue in excess of 1 billion Euros. Factoring up this rule of thumb over a number of drug manufacturing sites quickly demonstrates how super critical MRP II systems are. 

Software control deficiencies (lack of control on software configuration settings, software put into production with contaminant decision logic package errors, lack of root cause and preventative/corrective action, etc.)... 

Pharmaceutical and healthcare companies that invest in compnteiized systems need systems that are delivered on time and within bndget, and that fnUull bnsiness fnnctional and performance requirements. In their rush to place new prodncts and versions on the market, however, computer software and systems suppliers rarely deliver error-free products. In fact, some two thirds of lifecycle costs can be incnrred after delivery of the software and system to the users. Pharmaceutical and healthcare companies do not want lots of downtime, disruption, and escalating costs once a system has been delivered and implemented. And, of conrse, in GxP applications, any deficiencies will be of particular interest dniing regnlatory inspections. 

Various inborn errors of metabolism (Table 25-1) result from deficiencies or absence of some of the enzymes listed in Figure 25-9. Some of these are discussed later in the chapter. The relationship of carbohydrate metabolism to the production of lactate, ketone bodies, and triglycerides is also depicted in Figure 25-9. The pentose phosphate pathway, also known as the hexose monophosphate shunt, is an alternative pathway for glucose metaboUsm that generates the reduced form of nicotinamide-adenine dinucleotide phosphate (NADPH), which is used in maintaining the integrity of red blood cell membranes, in lipid and steroid biosynthesis, in hydroxylation reactions, and in other anabolic reactions. The complete picture of intermediary metabolism of carbohydrates is rather complex and interwoven with the metabolism of lipids and amino acids. For details, readers should consult a biochemistry textbook. 

The production of transgenic and knockout animals represents a powerful molecular biology technique whereby spontaneous inborn errors of metabolism (e.g., sulfite oxidase deficiency) have provided extensive and valuable insight into the identification of essential elements, for example molybdenum (O Dell and Sunde 1997). 

Equivalence of the quality of reprocessed material to the original material must also be evaluated and documented to ensure that the reprocessed batch will conform with all established standards, specifications and characteristics. There should be a sufficient investigation, evaluation and documentation to show that the reprocessed excipient is at least equivalent to other acceptable products and that the non-conformance did not result from an inadequate process. Obviously if the need for reprocessing resulted from human error, it will not reflect upon the process, but may indicate other deficiencies such as inadequate training or work instructions. 

Mutations leading to deficiencies in enzymes are usually referred to as inborn errors of metabolism, because they involve defects in the DNA of the affected individual. Errors in enzymes that catalyze reactions of amino acids frequendy have disastrous consequences, many of them leading to severe forms of mental retardation. Phenylketonuria (PKU) is a well-known example. In this condition, phenylalanine, phenylpyruvate, phenyllactate, and phenylacetate all accumulate in the blood and urine. Available evidence suggests that phenylpyruvate, which is a phenylketone, causes mental retardation by interfering with the conversion of pyruvate to acetyl-CoA (an important intermediate in many biochemical reactions) in the brain. It is also likely that the accumulation of these products in the brain cells results in an osmotic imbalance in which water flows into the brain cells. These cells expand in size until they crush each other in the developing brain. In either case, the brain is not able to develop normally. 

Alkaptonuria is a rare inborn error of metabolism caused by a lack of the enzyme homogentisic acid oxidase. The deficiency causes a failure to oxidize homogentisate, which is excreted in the urine in abundance. Polymerization of the metabolite, especially under alkaline conditions in the presence of oxygen, leads to the production of a black polymer. This makes the urine black if it is exposed to air for a few hours and in vivo, cartilage and other connective tissues become pigmented and take on an orange color (hence the name ochronosis for this state of the tissues the ocher color is readily seen postmortem). In later years the patients develop severe arthritis. 

The residence time for retinol in the test subject was predicted by the compartmental model to be 474 days. The residence time of 474 days is in excellent agreement with the 460 day MST that can be calculated from the data of Song et al. (1995) using the enrichment ratio method (Cobelli and Saccomani, 1992). Also, an MST of 105 to 337 days can be calculated from the half-life values (75 to 241 days) of body vitamin A reported by Sauber-lich et al. (1974) who depleted human subjects with vitamin A-deficient diets. At the same time the empirical description predicted the MST for retinol to be 26 days. While the reason for such a large discrepancy in MST (474 versus 26 days) between the compartmental model and the empirical description prediction is unclear, it is not likely to be accounted for by slight errors in estimating the final slope of the plasma retinol-d4 decay curve. Because the compartmental model embodies several features of retinol metabolism de novo production and release of retinol can occur in unobservable compartments, etc.) in addition to plasma retinol concentrations, its predicted MST is more likely to better reflect the dynamics of retinol metabolism. 

Bile acids have two major functions in man (a) they form a catabolic pathway of cholesterol metabolism, and (b) they play an essential role in intestinal absorption of fat, cholesterol, and fat-soluble vitamins. These functions may be so vital that a genetic mutant with absence of bile acids, if at all developed, is obviously incapable of life, and therefore this type of inborn error of metabolism is not yet known clinically. A slightly decreased bile acid production, i.e., reduced cholesterol catabolism, as a primary phenomenon can lead to hypercholesterolemia without fat malabsorption, as has been suggested to be the case in familial hypercholesterolemia. A relative defect in bile salt production may lead to gallstone formation. A more severe defect in bile acid synthesis and biliary excretion found secondarily in liver disease causes fat malabsorption. This may be associated with hypercholesterolemia according to whether the bile salt deficiency is due to decreased function of parenchymal cells, as in liver cirrhosis, or whether the biliary excretory function is predominantly disturbed, as in biliary cirrhosis or extrahepatic biliary occlusion. Finally, an augmented cholesterol production in obesity is partially balanced by increased cholesterol catabolism via bile acids, while interruption of the enterohepatic circulation by ileal dysfunction or cholestyramine leads to intestinal bile salt deficiency despite an up to twentyfold increase in bile salt synthesis, to fat malabsorption, and to a fall in serum cholesterol. 

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