By R. Stan. Holy Family College.
This is presumably owing to the inhibitory effect of ketones on uric acid excretion by the renal tubules (27) generic 100 mg kamagra chewable overnight delivery. This study (27) suggests that the combination of fasting and alcohol appears to be mutually potentiating with regard to their effect on uric acid metabolism order generic kamagra chewable online. After the introduction of a diet low in dairy products and high in fatty meats and carbohydrates in the early 1900s cheap kamagra chewable 100 mg with amex, an epidemic of obesity, hyperuricemia, and gout developed (28). Hyperuricemia and gout were rare among blacks in Africa, especially in rural areas where traditional agricultural and dairy-based diets were common. However, the frequency of hyperuricemia and gout is now increasing, particularly in urban communities, in parallel with hypertension and cardiovascular disease (30). The relationship between the consumption of purine-rich foods and the risk of devel- oping gout was evaluated in the Health Professionals Study (37). During the 12-year follow-up, validated semi-quantitative food-frequency questionnaires were used to obtain dietary information every 2 years. Little is known about the precise identity and quantity of individual purines in most foods, especially when they are cooked or processed (38). Additionally, the bioavailability of purines contained in different foods varies substantially. The variation in hyperuricemia and gout with different purine-rich foods may be explained by the variation in the amounts and types of purine content and their bioavailability for purine-to-uric-acid metabolism (31 34). Animal studies in this area have shown changes in purine content following the boiling and broiling of beef, beef liver, haddock, and mushrooms. However, although these cooking processes affect purine content, the nature of the changes is not clear. On the one hand, boiling high-purine foods in water can cause a break down of the purine-containing components (called nucleic acids) and eventual freeing up of the purines for absorption. For example, in some animal studies, where rats were fed cooked versus noncooked foods, the animals eating the cooked version experienced greater absorption and excretion of purine-related compounds. From this evidence, it might be tempting to conclude that cooking of high-purine foods actually increases the risk of purine overload. On the other hand, when foods were boiled, some of the purines were released into the cooking water and never ingested in the food. From this evidence, the exact opposite conclusion would make sense: Cooking of high-purines reduces the purine risk (39). However, a rigid purine-free diet can rarely be sustained for a long period of time. Moderation in dietary purines rather than a strict purine-free diet may be helpful (13). In a 12-year cohort study using biannual questionnaires, it was concluded that having more than two glasses of milk per day was associated with a 50% risk reduction in gout (37). This protective effect was only evident with low-fat dairy products, such as skim milk and low-fat yogurt. Because dairy products are low in purine content, dairy protein may exert its urate-lowering effect without providing the concomitant purine load contained in other protein sources such as meat and seafood. This apparent protective effect of dairy products against hyperuricemia may be multifactorial. In addition to the postulated uricosuric effect of milk proteins, the vitamin D content in milk may also play a key role. Whether the supplementation of vitamin D can prevent hyperuricemia has not yet been studied. The diet of the great apes consists of fruits and vegetation, with only small amounts of animal protein. Fruits According to a 1950 study of 12 people with gout, eating one-half pound of cherries or drinking an equivalent amount of cherry juice prevented attacks of gout. It is not known what compounds in cherries are responsible for these alleged actions. Neither total protein intake nor consumption of purine-rich vegetables was associated with an increased risk of gout. Another study compared the insulin-sensitivity indices between Chinese vegetarians and omnivores. The degree of insulin sensitivity appeared to correlate with years on a vegetarian diet (49). High-Protein Diets High-protein diets are associated with increased urinary uric acid excretion and may reduce the blood uric acid level (53 55). Increasing evidence supports the notion that it also may improve insulin sensitivity (60). One observational study followed gouty patients on a diet moderately decreased in calories and increased in protein (61). The authors suggested re-evaluation of the current dietary recommendations for patients with gout. They suggested that lowered insulin resistance could increase uric acid clearance from the renal tubule as a result of stimulation by insulin of tubular ion exchange (61). Forms of the latest popular diet programs include high-protein/high-fat/low- carbohydrate diets, such as Atkins, South Beach, and Zone. These diets encourage patients to take in foods that are rich in purine, such as meat and seafood, which have been associated with a higher risk of gout. Moreover, these diets are high in fat and can induce ketosis and subsequent hyperuricemia. The official Atkins Website (63) cautions patients about the potential flares of gout with the diet. Unfortunately, to date, there are no controlled studies on the impact of these ketogenic diets on serum urate levels and frequency of gout flares. However, odorless or odor-controlled garlic preparations have a high degree of activity and may be more appropriate. Autumn crocus (Colchicum autumnale) is the herb from which the drug colchicine was originally isolated. Colchicine, strong anti-inflammatory compound, is used as a conventional treatment for gout. However, other studies have failed to confirm the effectiveness of folic acid in treating gout (66). The effect of vitamin C on serum uric acid level was evaluated in a double- blind placebo-controlled study (67) of 184 participants who received either placebo or 500 mg per day of vitamin C for 2 months. Both groups had similar intakes of protein, purine-rich foods, and dairy products at baseline. The exact incidence of alcohol-induced gouty arthritis is not known, but it is estimated that half the gout sufferers drink excessively (69).
Tangles occur in living neurons but also are found as extracellular remains following nerve cell death buy 100mg kamagra chewable mastercard. The most salient are senile plaques that show degenerating neurites in proximity to large extracellular amyloid deposits purchase 100 mg kamagra chewable overnight delivery. Amyloid cores are made of polymerized amyloid beta (A`) peptide and contain a small variety of inflammatory From: Contemporary Clinical Neuroscience: Molecular Mechanisms of Neurodegenerative Diseases Edited by: M purchase kamagra chewable discount. As yet, however, no consen- sus exists regarding the primary pathogenic molecules. In this chapter, evidence is reviewed that strongly implicates a role for neurotoxins derived from A` peptides (for earlier reviews, see refs. Nonetheless, central roles also can be argued for inflammatory processes (23) and for cytoskeletal dysfunction linked to aberrant tau phosphorylation (24 26). Whichever molecular abnormality proves primary, the pathogenic phenomena are closely interrelated. Reciprocally, tau phosphorylation and microtubule A` Fibrils and Oligomers 3 dysfunction alter A` metabolism (30,31), and inflammatory glial proteins influence the nature of A`-derived toxic aggregates (refs. Emerging data show that toxic A`-derived fibrils and oligomers exert a selective impact on signal transduction molecules that are coupled physiologically to mechanisms of apoptosis and synaptic plasticity. The A` cascade is supported strongly by human pathology, transgenic modeling, and experimental nerve cell biology (see Milestones in Fig. Core Component of Alzheimer s Amyloid Is A` The first molecular milestone en route to the A` cascade hypothesis was reached in 1984 by Glenner and Wong (37). Their purification and analysis of the core component of Alzheimer s amyloid showed it to be a 4-kDa peptide, designated now as amyloid beta (A`). Although A`1 40 and A`1 42 are the predominant monomeric forms, peptides isolated from Alzheimer-afflicted brain tissue show length variations at both ends (46). The unusual tandem hydrophobic/hydrophilic domains of A` strongly influence its structure in solution and its biological properties (see Fibril Hypothesis, below). Several mutations in and around the A` sequence now are known to be pathogenic (50 56). Consistent with the A` cascade hypothesis, however, the established factors all contribute to anomalous accumulation of A` peptide. This is a salient feature because the more hydro- phobic A`1 42 has a particularly strong tendency to self-associate into neurotoxic multimers (see Fibril Hypothesis, below). Elevated A` accumulation is recapitulated in cell culture models that carry disease-associated transgenes (67 70). This, however, is not the case, as shown in the capstone discovery by Yankner et al. Prior to death, affected neurons show increases in phosphotau antigens associated with neuro- fibrillary tangles (28,29). Fibril Hypothesis The A` cascade hypothesis appears compelling: mutations and other agents that cause Alzheimer s disease do so by producing molecules that kill neurons. Nonetheless, debate over the A` cascade hypothesis has been contentious (81,82) and remains ongoing (83). Some cells, such as glia, naturally resist the degenerative action of A` (86), and 6 Klein subclones of neuronal cell lines can be selected for resistance (87 89). The state of neuronal differentiation further determines the outcome of exposure to A` (29,74). Factors that influence sensitivity may include cell cycle with- drawal, increased demand for trophic support, switchover from anaerobic to aerobic metabolism, or altered expression of signal transduction molecules. A second factor is the inherent difficulty in controlling the conformation of monomeric A`, a molecule with tandem hydrophilic and hydrophobic domains. Many investigators have simplified experiments through use of A`25 35, a hydrophobic 11-mer that is a reliable toxin at high doses (90,91). The 11-mer is not found naturally, however, and may only partially mimic the cellular impact of full-length A`. Synthetic A`1 40 and A`1 42 are available commercially now at reasonable cost, and means to obtain recom- binant peptide have been described (92). Earlier purity problems with commercial A`42 have been largely overcome, although lot-to-lot variations in toxic efficacy continue to exist. The potential of A` for alternative states is reminiscent of prions, which can be innocuous or deadly, depending on protein conformation (94). Discovery of this relationship has played a significant role in overcoming objections to the A` cascade hypothesis. Self-Association of A` Is Critical for Neurotoxicity Major findings of Cotman, Yankner, and their colleagues established that synthetic A` is neurotoxic only after it self-associates into larger assemblies (84,95). Toxic solutions examined by electron microscopy or atomic force microscopy show abundant fibrils (84,96,97). It has been proposed, therefore, that fibrillar forms of A` are required for neurotoxicity. One such A` Fibrils and Oligomers 7 condition, for example, would be anomalous abundance of monomer due to genetic factors. Fibrillogenesis has been the subject of intense investigation (for reviews, see refs. For fibrils to form in vitro, A`40 must be above a critical concentration (50 M or more; see reviews in refs. A lag phase also occurs (kinetic solubility), during which peptide slowly undergoes prerequisite associations. The more hydrophobic A`42 converts to fibrils at lower critical concentrations (5- M doses) and shows little or no kinetic solubility. The abundance of amyloid fibril deposits in Alzheimer s brain and in transgenic animals gives prima facie evidence that local A` concentrations in vivo exceed critical concentration. Some reports suggest that fibrils can kill neurons at nanomolar doses of A` (74,91), but concentrations used in typical nerve cell biology experi- ments exceed 20 M (in total molarity of A`). Although this dose may seem high, molarity has little meaning with respect to insoluble assemblies such as fibrils. Because immature or diffuse plaques, thought to comprise amorphous A` supramolecular assemblies, do not trigger local neuronal degeneration (108 110), degenerative effects may depend on particular configurations of aggregated A` (84). The persuasiveness of the A` fibril hypothesis has motivated an intense search for compounds that inhibit fibril toxicity. Several promising fibril- blocker neuroprotectants (111 113) have been found, including certain dyes (84,114,115) and small peptides that act as `-sheet breakers (116). Electron microscopy shows fibrils from aggregated A` (arrows) extend to the plasma membrane of a neuron-like human cell line (arrowheads). Fibril Hypothesis Is Powerful but Imperfect An extensive literature focuses on fibril neurotoxicity. A particular problem with the fibril hypothesis is the imperfect correla- tion between amyloid abundance and dementia. Although postmortem analyses are not optimum for answering questions of cause-and-effect, attempts to correlate pathological markers with dementia have challenged as well as supported the A` fibril hypothesis. Some studies have concluded that decreased synaptic density and the abundance of tangles are more germane than plaques to the progression of dementia. Various explanations have been offered to account for the imperfect correlation (121,122), including the argument that better data analysis and selection of plaque subtype show improved correlation (123).
Common Diseases of the Conjunctiva and Cornea 49 Other Infective Agents keratoconjunctivitis have a higher risk than normal for the development of herpes simplex The conjunctiva can be affected by a wide keratitis; the condition is also associated with variety of organisms buy cheap kamagra chewable on line,some of which are too rare the corneal dystrophy known as keratoconus or to be considered here purchase kamagra chewable 100mg, and sometimes the conical cornea cheap 100mg kamagra chewable free shipping. They are likely to develop skin infected conjunctiva is of secondary importance infections and chronic eyelid infection by to more severe disease elsewhere in the rest of staphylococcus. It be avoided if possible because of their side can be accompanied by conjunctivitis when effects. The infec- predisposed individuals and aggravate herpes tion is usually easily eliminated by curetting simplex keratitis. Infection from Phthirus pubis (the pubic louse) involving the lashes and Vernal Conjunctivitis (Spring Catarrh) lid margins can initially present as conjunc- Some children with an atopic history can tivitis but observation of nits on the lashes develop a specic type of conjunctivitis charac- should give away the diagnosis. The child tends to develop Allergic Conjunctivitis severely watering and itchy eyes in the early spring, which can interfere with schooling. Several types of allergic reaction are seen on the Eversion of the upper lid reveals the raised conjunctiva and some of these also involve the papillae, which have been likened to cobble- cornea. Occasionally, the cornea is also involved, initially by punctate keratitis but sometimes it This is simply the commonly experienced red can become vascularised. It is often necessary and watering eye that accompanies the sneezing to treat these cases with local steroids, for bouts of the hay fever sufferer. The eyes are itchy example, prednisolone drops applied if needed and mildly injected and there might be con- every two hours for a few days,thus enabling the junctival oedema. The dose can then be vasoconstrictors, such as dilute adrenaline or reduced as much as possible down to a main- naphazoline drops, can be helpful; sodium tenance dose over the worst part of the season. Atopic Conjunctivitis Unfortunately,patients with asthma and eczema can experience recurrent itching and irritation of the conjunctiva. Less severe cases can respond well to spreads into the cornea, drawing a triangular sodium cromoglycate drops; these can be band of conjunctiva with it. The eye becomes useful as a long-term measure and in prevent- irritable because of associated conjunctivitis ing but not controlling acute exacerbations. Pterygium Secondary Conjunctivitis is more common in Africa, India, Australia, Inammation of the conjunctiva can often China and the Middle East than in Europe. It is be secondary to other more important pri- rarely seen in white races living in temperate cli- mary pathology. Treatment is by surgical excision if the possible underlying causes of this type of cornea is signicantly affected with progression conjunctivitis: towards the visual axis; antibiotic drops might be required if the conjunctiva is infected. Non- Lacrimal obstruction infective inammation of pterygium is treated Corneal disease with topical steroids. Examples of this are the red eye unilateral purulent conjunctivitis and it is of renal failure and gout, and also polycythemia important to consider this possibility in recal- rubra. The association of conjunctivitis, arthri- citrant cases because early resolution can be tis and nonspecic urethritis makes up the triad achieved simply by syringing the tear ducts. Some diseases cause Corneal ulceration from a variety of causes is abnormality of the tears and these have already often associated with conjunctivitis and here been discussed with dry eye syndromes, the the treatment is aimed primarily at the cornea. Thyrotoxicosis is a more common ecially in the case of entropion, when the defor- mity is not present all the time. A special type of degenerative change is seen in the conjunctiva, which is more marked in hot, dry, dusty climates. It appears that the com- bination of lid movement in blinking, dryness and dustiness of the atmosphere and perhaps some abnormal factor in the patient s tears or tear production can lead to the heaping up of subconjunctival yellow elastic tissue, which is often inltrated with lymphocytes. The lesion is seen as a yellow plaque on the conjunctiva in the exposed area of the bulbar conjunctiva and usually on the nasal side. Common Diseases of the Conjunctiva and Cornea 51 dence of this occurrence on windy, dry days. Small foreign bodies also become embedded as the result of using high-speed grinding tools without adequate protection of the eyes. The dentist s drill can also be a source of foreign bodies, but the most troublesome are those particles that have been heated by grinding or chiselling. It is important to have some under- standing of the anatomy of the cornea if one is attempting to remove a corneal foreign body. One must realise, for example, that the surface epithelium can be stripped off from the under- lying layer and can regrow and ll raw areas with extreme rapidity. Under suitable cond- itions the whole surface epithelium can reform in about 48 h. The layer underlying,or posterior, to the surface epithelium is known as Bowman s membrane and if this layer is damaged by the injury or cut into unnecessarily by overzealous use of surgical instruments, a permanent scar might be left in the cornea. When the epithelium alone is involved, there is usually no scar, and healing results in perfect restoration of the optical properties of the surface. It should be remembered that if the retraction, conjunctival oedema and proptosis, cornea has been perforated, the risk of intra- are usually more evident. A rather persistent ocular infection or loss of aqueous dictates that type of conjunctivitis is seen in patients with the wound should be repaired under full sterile acne rosacea. The cornea becomes Signs and Symptoms invaded from the periphery by wedge-shaped Patients usually know when a foreign body has tongues of blood vessels associated with recur- gone into their eye and the history is clear-cut rent corneal ulceration. Occasionally, the complaint is conjunctivitis is seen less commonly now, simply a red sore eye, which might have been perhaps because it responds well to treatment present for some time. Spotting these corneal with the combination of systemic doxycycline, foreign bodies is really lesson number one in lubricants for associated dry eye and the judi- ocular examination. Usually, it is important basic principles of examining the also necessary to instruct the patient to clean anterior segment of the eye. Most foreign bodies the lids and perform lid hygiene, as such can be seen without the use of the slit-lamp patients are often also affected by blepharitis. There is no doubt that the corneal epi- thelium heals more quickly if the eyelids are splinted in this way. It is usually advisable to see Treatment the patient the following day if possible to make The aim of treatment is,of course,to remove the sure that all is well, and if the damaged spot on foreign body completely. Sometimes this is not the cornea is no longer staining with uor- as easy as it might seem, especially when a hot escein, the pad can be left off. In should be continued at least three times daily instances when it is clear that much digging is for a few days after the cornea has healed. The going to be needed, it can be prudent to leave visual acuity of the patient should always be the rust ring for 24 h, after which it becomes checked before nal discharge. The procedure for removing a There are one or two factors that should foreign body should be as follows: the patient always be borne in mind when treating patients lies down on a couch or dental chair and one or with corneal foreign bodies: in most instances, two drops of proparacaine hydrochloride 0. The doctor will also usually require some optical aid in the form of special magnifying spectacles, for example Bishop Harman s glasses or the slit-lamp. Many foreign bodies can be easily removed with a cotton-wool bud (particularly those lodged under the upper lid), but otherwise at the slit- lamp a 25-gauge orange needle angled nearly perpendicular to the plane of the iris can be used to lift off the foreign body.