The sensory function plays an important role in everyday life, because it brings the pleasure of touch, smell, taste, see and listen.
The alteration of one of 5 senses disrupts the quality of life.
The loss of taste may lead to problems such as loss of appetite with consequent a weight loss and nutritional deficiencies.
The taste and the sense of smell are with difficulty dissociable because these two senses are aroused when feeding.
In the U.S., it is estimated that every year approximately two hundred thousand people consult for disorders related to taste and smell
Different etiologies may lead to loss of taste :
The modifications of the saliva quantitative or qualitative constitute an obstacle to the routing of substances into contact with the taste bud and helps to explain the taste disorders observed in the Gougerot-Sjögren syndrome or during an anticholinergic treatment.
Nutritional deficiencies and vitaminic (vitamin B3 and B12), treatments such as radiotherapy and cytotoxic drugs can interrupt the cycle of regeneration of taste buds while keeping intact the lingual epithelium.
But the epithelium can itself be altered, during iron deficiencies, vitaminic deficiencies (vitamin B12), by viral or mycotic infections.
The transduction of the signal at the level of the gustative cells can be also modified by some medicines like the calcic inhibitors.
Finally the neurogene attack, by touching the way leading the signal of the bud to the cortex, can be affected to any level, by a pathological phenomenon or a medicinal unwanted effect of toxic nature or pharmacological.
If we observe the surface of the tongue, we distinguish, even with the naked eye, very small circular protrusions of various shapes: the lingual papillae.
The receivers of the taste are located in some of these papillae (the fungiform papillae and especially the calyciform). In the thickness of the epithelium covering the papilla, open many microscopic pores which correspond to the buds of the taste. It is inside these pores that are situated the sensory cells which receive stimuli at the villosities level.
On the opposite side, the gustative cell goes on by a nerve fiber.
All the fibers stemming from sensory cells reunite in nerves (the lingual nerve and the glossopharyngeal nerve) which lead the gustative nervous messages to the brain area of the taste where they are registered and recognized.
The sense of taste cannot distinguish as four fundamental flavours: sweet, salty, bitter and acid. The other flavours are only mixtures.
The mechanism of the taste is connected to the exchanges of sodium and potassium in taste buds. The pathogenic mechanisms potentially associated to the taste disorders are firstly a local atrophy of taste buds, a rupture or injury of physical cause or chemical, secondly a damage caused in the projections of neurons, thirdly an imbalance of cellular regeneration cycle and et fourthly a modification of the receptors due to a local change as for example the salivation.
The saliva is the solubilizer flavors agent allowing them to make better contact with the taste buds. The reduced flow of saliva (xerostomia) is a problem frequently met during the taking of medicines with anticholinergic or adrenolytic action and is thus associated with the decrease of the taste.
Furthermore, not only the patients present a problem of salivation, a problem of dysgeusia, but also a problem of chewing and feeding, it is recognized in many scientific publications that these factors are closely linked. The xerostomia is also a big factor of polycaries in the elderly.
Main medicines able to induce taste disorders.
Cardio-vascular (IECA, BCC, Anti-arrythmic, Diuretics, Hypoglycemics, Beta-Blockers), Anti-infective (Cephalosporin, Macrolides, Metronidazole, Penicillins, Quinolones, Sulfamides, Tetracyclines.), Anti-fungal, Anti-viral (didanosine, zidovudine...
AINS : ibuprofen, indomethacin, diclofenac...), Hypoglycemics (Biguanides, tolbutamide, glipizide, insulin...), Antihistamines and decongestants, Psychotropic (Anxiolytics, hypnotics,Antidepressants, Antipsychotics, Lithium), Muscle relaxants, Anti-Parkinson, Anti-convulsants, Immunosuppressants,
Antiemetics, Anti-H2, Antispasmodic
In the long term, a medicated dysgeusia affects largely the quality of life of the patient. Number of medicines can affect the taste if we considers the dysgeusia as a possible consequence of xerostomia induced by medicines.
However, certain classes of medicines can cause impaired perception of taste without that xerostomia is involved.
The differentiation, growth, the architectural and functional integrity of taste buds and their receptors, depend on salivary proteins (particularly the Gustine - zinc-dependent). The medicines that alter the synthesis, architecture or the activity of these proteins can alter the taste.
Various physiopathological mechanisms are at the origin of the gustative distortions induced by medicines. By altering the body homeostasis, the medicines causes a cascade of biochemical events or chemosensory.
These biological changes can thus modify sensory perception because there is rupture of the balance required for the optimal functioning of taste buds.
The most frequent are a zinc deficiency by chelation via medicines, then it can have a alteration of the metabolism of the zinc (at the molecular level) but also by an alteration of the zinc (at the enzymatic level) as essential cofactor of the gustine (the protein of the taste buds which maintains the homeostasis and the integrity of the gustative receptors).
There may have also an excretion of the medicine by the saliva, an inhibition of the regeneration of the gustative cells, an interference with the second messenger, interference with the cytochrome P450, a modification of the Ionic flows of the calcic or sodic channels, inhibition of the AMPc, lesion of the double lipid membrane, etc...
Data from the scientific literature shows that the magnitude of the reported cases should particular make us focus more attention on this type of unwanted effect so as to better manage and help patients in gustative distress.
A recent Japanese study estimates at 11 % the proportion of elderly reached by taste disorders related to the taking of medicines.
Used in the upper aerodigestive tract cancers, the irradiation is at the origin of hyposialia by direct lesion of the salivary glands without sparing the gustative cells. The saliva becomes rare and very viscous involving at once a loss of the lubricating power and the solvent power of sapid substances.
A prolonged irradiation can cause a permanent loss of taste by fibrosis of the salivary glands.
To mitigate the oral drought accompanying these therapeutic, sialagogues or saliva substitutes may be prescribed.
The deficiencies in zinc, B3, B12, copper, iron ... and vitamin A may be responsible for hypogeusia because they intervene in the normal development of taste cells.
The zinc is a key trace element in the treatment of dysgeusia.
Numerous studies demonstrate the close link between a sufficient zinc rate and its role in the taste.
Dr Hentkin, director of - The taste and smell clinic - at Washington is considered a specialist in the U.S. taste. He studied the role of carbonic anhydrase VI ( the gustine ), a zinc-dependent enzyme secreted by the salivary glands.
This enzyme plays a key role in in taste function and its activity is closely linked to the presence of zinc sufficiency. He believes that zinc deficiency is not always related to a lack of supply but also to a bad assimilation of this one.
Various studies of Dr Hentkin show the efficiency of the zinc in its action of stimulation of the enzyme carbonic anhydrase VI and in the capacity to regenerate the taste bud (recovery of the morphology) this recovery of the taste and smell is associated at an elevation of zinc level in saliva, urines and plasma.
Its dosage is difficult. Indeed, the revealing of a zinc deficiency is not easy because a normal rate of zinc in the plasma is not synonymic of deficiency. The plasma rate detects only the severe deficiencies and not the sub-deficiencies.
The American researchers recommend to measure the zinc rate in lymphocytes in order to have a more sensitive test. But these dosages are practicable only in a few laboratories in the USA and are often expensive.
It seems more implied in the olfactive disorders; however, the pravastatin was implicated in cases of dysgueusie by decrease of the rate of vitamin A. The onset of the disorder appears between 2 and 6 weeks of treatment at a dose between 10 and 20 mg / day, and disappears in 1 to 4 weeks after cessation.
Some medicines alter the synthesis of proteins, what entails the decrease of the cellular renewal; as this renewal is fast, a disorder of the taste can be noticed.
A Japanese study made by a team of ENT, put in evidence the relation between deficiency of the activity of SOD in the serum and the saliva in patients presenting disorders of smell provoked by a chronic sinusitis or a banal flu.
The role of copper is not well defined in taste disorders. However, ageusies are common with certain specialties being able to induce a copper deficiency.
D-penicillamine, used in the long term in patients reached by a rheumatoid polyarthritis, is responsible for a sensation of transient metallic taste but relapsed to each taken.
This disorder affects an average of 25-50% of patients, with doses above 900 mg/d.
Some total agueusies, reversible over two or three months are even possible
Gold salts and antithyroid of synthesis are also involved in copper deficiencies.
Several studies have shown a disturbance of taste in the context of smoking.
The tobacco use seems to decrease the recognition of the acid flavour, much more than the other flavours, and the bitter taste in a lesser degree.
This disturbance in smokers, may be due to several factors.
The deficiency in vitamin B12 is observed in smokers, can be at the origine of disorders of taste, since this vitamin is involved in the regeneration of taste bud and lingual epithelium.
We also know that exist in smokers, a toxicity of heavy metals such as cadmium chloride, which has an adverse impact on the mitochondria and the endothelium, and enters into competition with zinc.
This has particularly been studied in pregnant women smoker's. Indeed, competitiveness of zinc-cadmium in placenta creates a zinc deficiency (cofactor of many enzymes) noxious at the level of the placenta. So if the competition exists between cadmium and zinc in placenta, it could also cause zinc deficiency in smokers, at the origin of taste disorders.
On the other hand, we know that smoking through nicotine, leads to a sub-weight in smokers. This is due to a loss of body fat at the beginning of smoking attributed to the increased of energy expenditure linked to tobacco consumption.
It is also possible that taste disorders are the cause of a decrease in caloric intake in smokers. Indeed, it has been shown that taste disorders are associated to a decrease of the calorie intake, to an increase of the nutritional risk, and to a reduction of the consumption in fruits and in vegetables as in smokers.
The taste disorders leads to a deficiencies in calcium and vitamins A and C. The deficiency in vitamin C is also noticed in smokers.
Furthermore, the increase of the labial and lingual heat induced by smoking could alter locally the lingual epithelium and so affect the taste of the smoker.
The presence of a metallic taste is often the first symptom of a dental metal poisoning.
The presence of several metals of different composition often causes phenomena electrogalvanic with diffusion of metal ions in saliva.
Zinc, B3, B12, cooper, iron... :
- ULTRA VITA MINERAL - 2 caps per day
- Cod liver oil- 1 capsule per day : natural source of vitamin A which prevents any risk of overdose and allows optimum assimilation
- SOD forte - dosed at 100 mg, 1 cp per day : boost the anti-radical function and protect the tissular protein regulation of the metabolism at any level and treat the olfactive disorders which can be associated to the taste disorders.TMD Toxic Metal Detox - 1 capsule twice daily with meals. : when the check up of intolerance and / or poisoning in dental metals are positive, associated to important intra-oral galvanic currents, the removal of metals will be associated with the protocol of treatment.
Many testimonies concerning the iatrogenic disorders of the taste can be collected in the literature.
These data, although often incomplete, based on little rigorous experimental protocols or for a small number of patients, demonstrate that this unwanted effect is very common, and that it interests many therapeutic.
It can certainly be considered in certain conditions as a sequela of medicinal treatment. While in most instances, the taste disorder is dose-dependent and disappears after discontinuation of treatment more or less quickly, in some cases it can persist and require the implementation of a specific corrective treatment.
It is important to realize that a taste disorder, particularly if sustained, can have an impact on quality of life of patients who suffer. This can lead to noncompliance, but mostly to nutritional deficiencies by anorexia, exacerbations of diabetes, hypertension, or even contribute to depressions.
The main mechanisms involved are processes which act either on the environment of taste cells (saliva), soit either directly or indirectly on the development and multiplication of these receptors (deficiency in trace elements and vitamins, inhibition of DNA synthesis, chelating zinc ...), or which prevent a transmission of nerve impulses in good conditions (inhibition of On-Off system, inhibition of cytochrome P450, inhibition of ion channels, action on the second messengers).
These aspects of molecular biology allow to understand better how medicines can affect the taste, and how it is possible to control these disorders.
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