Sources of Pyrogens Pyrogen definition Classification of Pyrogens Properties of Endotoxins Chemical Nature of Endotoxin Biological properties of endotoxin Physical properties of endotoxins Mechanism of pyrogens References
PYROGENS DEFINITION: Pyrogens are fever producing substances, which are metabolic products of microorganisms. Chemically, they are lipid substances associated with a carrier molecule, which is usually a polysaccharide. The carrier may also be a peptide. These carriers increase the solubility of the lipid. Pyrogens are produced by many microorganisms including bacteria, yeasts and moulds. Most potent pyrogens are the endotoxins produced from the cell walls of the Gram- negative bacteria.
Sources of Pyrogens: Solvents, drugs, additives apparatus used in manufacture, containers; all or any of these may be sources of pyrogens. The method of storage in between preparation and sterilization also may cause the development of pyrogens. Hence every item must be apyrogenic and method of storage must not allow any bacterial growth.
Classification of PyrogensThe scientific literature divides Pyrogen in twobroad classes. Exogenous Pyrogen ( Exotoxins) Endogenous Pyrogen (Endotoxin)
Exogenous Pyrogen ( Exotoxins) Non microbial Pyrogens Microbial Pyrogens Non host host origin origin Bacteria (killed or live), FungiNon microbial exogenous Non microbial exogenous (killed or live), plasmodiapyrogens of nonhost pyrogens of host origin include (malarial parasites),andorigin include Antigen-Antibody complexes, viruses(live) can all act aspharmacologic agent like products of lymphocytes and pyrogens, additionally bacterialbleomycin, colchicin and metabolic Products of products, including streptococcalpolynucleotide poly- 1: C, androgenic steroids endotoxin, staphylococcal endotoxins. Microbial exogenous pyrogens Most of non microbial pyrogen are much more of a problem for forms produce fever by inducing pharmaceutical manufacturers; the synthesis and release of the lipopolysaccharide in the endogenous pyrogen from host endotoxin is toxic in small phagocytic cells. Quantities. 6
Endogenous Pyrogens Exogenous pyrogen dont act directly on the thermoregulatory center of the hypothalamus of the brain to cause fever, Instead exogenous pyrogens stimulates the production of intermediate heat-labile, Protienacious, mediator substances,Since this mediator substance was first isolated from granulocytes, It was initially called granulocytic pyrogen or sometimes leukocytic pyrogen,After the mediator substance was found in the circulatory serum of febrile rabbits it was called endogenous pyrogenEndogenous pyrogen are produced by blood monocytes, Eiosinophils,alveolarmacrophages and fixed- tissue macrophages such as splenic sinusoidal cells andhepatic kupffer cells,When injected in to animals, It also induced hepatic acute-phase proteinsynthesis,caused decrease in plasma iron and zinc levels produced neutrophilia,stimulated serum amyloid, a protein synthesis and augmented T cells response tomitogen and antigens. 7
The biological activity of endotoxin is associated with the lipopolysaccharide (LPS). Toxicity is associated with the lipid component (Lipid A) and immunogenicity is associated with the polysaccharide components. The cell wall antigens (O antigens) of Gram-negative bacteria are components of LPS. LPS elicits a variety of inflammatory responses in an animal and it activates complement by the alternative (properdin) pathway, so it may be a part of the pathology of Gram-negative bacterial infections.
Endotoxin has a polysaccharide structure that iscovalently bound to a lipid component, called lipid AThe polysaccharide component is composed of twodistinct parts, the core oligosaccharide that is connectedto lipid A and a longer oligosaccharide O-specific chainthat is attached to the core and is the outer most part ofthe LPS Complex.The O-specific chain is the most variable component ofthe complex. 9
It consist of 20-40 repeating units that include up to the eight sugars, and it is responsible for the specific immune reaction that each type of gram- negative bacteria is able to evoke in a host , The core oligosaccharide is much less variable than O-specific chain and its influence on the host is less profound,
The lipid A is the least variable components of LPS. It consists of adisaccharides of glucosamine which is the highly substituted with amide-linked and structure-linked long chain fatty acids,Lipid A is the most interesting portion of LPS because it is responsible forthe vast majority of the harmful and the beneficial biological activities thathave been attributed to endotoxins .
BIOLOGICAL PROPERTIES OF ENDOTOXINS: Endotoxins are potent substances which elicit a broad spectrum of the harmful physiologic responses, Profound alteration in organ function, such as hypotension and disseminated intravascular coagulation, which can lead to severe morbidity or death But on the other hand endotoxins are also active stimulators of the mammalian defense system, This capacity can enhance the body’s capacity to cope with both microbial infections and malignant tumors.
Physical properties of endotoxins It is important to be aware of the various physical properties of endotoxin in order to understand why they change their behavior when placed into different environments, An understanding of these physical properties is also essentials for designing effective process for depyrogenation. Heat stability Size Molecular weight Electrostatic properties
Mechanism of pyrogens A trigger of the fever, by pyrogen, causes a release of prostaglandin E2 (PGE2). PGE2 then in turn acts on the hypo Temperature is ultimately regulated in the hypothalamusthalamus, which generates a systemic response back to the reset of the body, causing heat-creating effects to match a new temperature level A pyrogen is a substance that induces fever. These can be either internal (endogenous) or external (exogenous) to the body. The bacterial substance lipopolysaccharide (LPS), present in the cell wall of some bacteria, is an example of an exogenous pyrogen.
Cytokines (especially interleukin 1) are a part of the innate immune system, are produced by phagocytic cells, and cause the increase in the thermoregulatory set-point in the hypothalamus. Other examples of endogenous pyrogens are interleukin 6 (IL-6), and tumor necrosis factor- alpha. Fever signals sent to the DMH and rRPa lead to stimulation of the sympathetic output system, which evokes non-shivering thermogenesis to produce body heat and skin vasoconstriction to decrease heat loss from the body surface. It is presumed that the innervation from the POA to the PVN mediates the neuroendocrine effects of fever through the pathway involving pituitary gland and various endocrine organs
References Encyclopedia of Pharmaceutical Technology, Volume:13,By James Swarbick & James Boylan. Indian Pharmacopoeia 2007,Vol.-1,Appendice-, British Pharmacopoeia 2007, United state pharmacopoeia Remington( The science and practice of pharmacy), Volume-I , Page no.562,832. The text book of pharmaceutical Technology, By Leon Lachman, Kenneth Todar online textbook of Bacteriology