Introduction
Penicillin is a group of antibiotics that is derived from the fungal penicillin. It was among the first drugs to be effective against many previously serious diseases. Some of those diseases are between infections caused by staphylococci and streptococci. It acts as an antibiotics by its action of inhibiting the cell wall synthesis when it combined with transpeptidase responsible for cross, linking of the peptidoglyca. It is a bactericidal agent and the activity is dependent on an intact β-lactum nase (Ochei et al., 2008).
Penicillin structure includes a β -lactum ring with four members which gives it a specific potency. Alteration of the side chain can cause formation of its derivatives which are “Ampicillia” “Amoxyclin” Cloxacillins” “Augumentin” and “Impenem”. (Ochei et al., 2008). Natively penicillin can be found in cheese and old bread because it is derived from mold.It can also be taken in orally as drug. It is actively excrted and about 80% of a penicillin dose is cleared from the body within three to four hours of administration (Silverthorn, 2004).
The liver has very complicated functions, and the most important is the detoxitication of drugs such as antibiotics and its metabolites. Some antibiotics can cause allergic reactions while others can cause direct damage to the liver. When antibiotics accumulates, they could become toxic to the body organs and their functions can change drastically from its original purpose (Zhang. 2005.)
What is penicillin?
Penicillin is a group of antibiotics which include penicillin G (intravenous use), penicillin V (oral use), procaine penicillin, and benzathine penicillin (intramuscular use). Penicillin is derived from Penicillium fungi and it is among the first medications to be effective against many bacterial infections caused by staphylococci and streptococci. Penicillins are still widely used today, though many types of bacteria have developed resistance following extensive use. All penicillins are β-lactam antibiotics (Garrod, 2010).
There are several enhanced penicillin families which are effective against additional bacteria; these include the antistaphylococcal penicillins, aminopenicillins and the antipseudomonal penicillins. But the term “penicillin” is often used generically to refer to benzylpenicillin (penicillin G, the original penicillin found in 1928), procaine benzylpenicillin (procaine penicillin), benzathine benzylpenicillin (benzathine penicillin), and phenoxymethylpenicillin (penicillin V). Procaine penicillin and benzathine penicillin have the same antibacterial activity as benzylpenicillin but act for a longer period of time. Phenoxymethylpenicillin is less active against gram-negative bacteria than benzylpenicillin. Benzylpenicillin, procaine penicillin and benzathine penicillin are given by injection (parenterally), but phenoxymethylpenicillin is given orally (Rossi, 2006).
While the number of penicillin-resistant bacteria is increasing, penicillin can still be used to treat a wide range of infections caused by certain susceptible bacteria, including Streptococci, Staphylococci, Clostridium, and Listeria genera. The following list according to Bud (2009) illustrates minimum inhibitory concentration susceptibility data for a few medically significant bacteria:
- Listeria monocytogenes: from less than or equal to 0.06 μg/ml to 0.25 μg/ml
- Neisseria meningitidis: from less than or equal to 0.03 μg/ml to 0.5 μg/ml
- Staphylococcus aureus: from less than or equal to 0.015 μg/ml to more than 32 μg/ml
Historical background on penicillin
The discovery of penicillin is attributed to Scottish scientist and Nobel laureate Alexander Fleming in 1928. He showed that, if Penicillium rubens were grown in the appropriate substrate, it would exude a substance with antibiotic properties, which he dubbed penicillin. This serendipitous observation began the modern era of antibiotic discovery. The development of penicillin for use as a medicine is attributed to the Australian Nobel laureate Howard Walter Florey, together with the German Nobel laureate Ernst Chain and the English biochemist Norman Heatley (Houbraken et al., 2011).
Fleming noticed a Petri dish containing Staphylococcus that had been mistakenly left open, was contaminated by blue-green mould from an open window, which formed a visible growth. There was a halo of inhibited bacterial growth around the mould. Fleming concluded that the mould released a substance that repressed the growth and caused lysing of the bacteria (Lax, 2009).
Scientists now suspect that Fleming’s story of the initial discovery of the antibacterial properties of the penicillium mould is inaccurate. With a modern understanding of how the bacteria and the mould interact, scientists know that if bacteria were already present on the petri dish they would have inhibited the growth of the mould and Fleming would not have noticed any mould on the plate at all. A more likely story is that a spore from a laboratory one floor below, run by C. J. La Touche, was transferred to Fleming’s petri dish before the bacteria were added. At the time of the initial discovery La Touche was working with the same mould found in Fleming’s petri dish.
Once Fleming made his discovery he grew a pure culture and discovered it was a Penicillium mould, now known to be Penicillium notatum. Fleming coined the term “penicillin” to describe the filtrate of a broth culture of the Penicillium mould. Fleming asked C. J. La Touche to help identify the mould, which he incorrectly identified as Penicillium rubrum (later corrected by Charles Thom). He expressed initial optimism that penicillin would be a useful disinfectant, because of its high potency and minimal toxicity in comparison to antiseptics of the day, and noted its laboratory value in the isolation of Bacillus influenzae (now called Haemophilus influenzae) (Howie, 2006).
Structure of penicillin
The term “penam” is used to describe the common core skeleton of a member of the penicillins. This core has the molecular formula R-C9H11N2O4S, where R is the variable side chain that differentiates the penicillins from one another. The penam core has a molecular weight of 243 g/mol, with larger penicillins having molecular weights near 450—for example, cloxacillin has a molecular weight of 436 g/mol. The key structural feature of the penicillins is the four-membered β-lactam ring; this structural moiety is essential for penicillin’s antibacterial activity. The β-lactam ring is itself fused to a five-membered thiazolidine ring. The fusion of these two rings causes the β-lactam ring to be more reactive than monocyclic β-lactams because the two fused rings distort the β-lactam amide bond and therefore remove the resonance stabilisation normally found in these chemical bonds (Howie, 2006).
Mechanism of operation of penicillin
Penicillin is a widely used antibiotic prescribed to treat staphylococci and streptococci bacterial infections. Penicillin belongs to the beta-lactam family of antibiotics, the members of which use a similar mechanism of action to inhibit bacterial cell growth that eventually kills the bacteria (Parascandola, 2010)
Bacteria cells are surrounded by a protective envelope called the cell wall. One of the primary components of the bacterial cell wall is peptidoglycan, a structural macromolecule with a net-like composition that provides rigidity and support to the outer cell wall. In order to form the cell wall, a single peptidoglycan chain is cross-linked to other peptidoglycan chains through the action of the enzyme DD-transpeptidase (also called a penicillin binding protein—PBP). Throughout a bacterial lifecycle, the cell wall (and thus the peptidoglycan crosslinks) is continuously remodeled in order to accommodate for repeated cycles of cell growth and replication (Baldwin et al., 2007)
According to Brakhage (2008), penicillins and other antibiotics in the beta-lactam family contain a characteristic four-membered beta-lactam ring. Penicillin kills bacteria through binding of the beta-lactam ring to DD-transpeptidase, inhibiting its cross-linking activity and preventing new cell wall formation. Without a cell wall, a bacterial cell is vulnerable to outside water and molecular pressures, and quickly dies. Since human cells do not contain a cell wall, penicillin treatment results in bacterial cell death without affecting human cells.
Gram-positive bacteria have thick cell walls containing high levels of peptidoglycan, while gram-negative bacteria are characterized by thinner cell walls with low levels of peptidoglycan. The cell walls of gram-negative bacteria are surrounded by a lipopolysaccharide (LPS) layer than prevents antibiotic entry into the cell. Therefore, penicillin is most effective against gram-positive bacteria where DD-transpeptidase activity is highest (Sheehan, 2007).
Effects of penicillin
Common adverse drug reactions (≥ 1% of people) associated with use of the penicillins include diarrhoea, hypersensitivity, nausea, rash, neurotoxicity, urticaria, and superinfection (including candidiasis). Infrequent adverse effects (0.1–1% of people) include fever, vomiting, erythema, dermatitis, angioedema, seizures (especially in people with epilepsy), and pseudomembranous colitis (Rossi, 2006)
About 10% of people report that they are allergic to penicillin; however, 90% of this group are not actually allergic. Serious allergies only occur in about 0.03% (Gonzalez, 2015). Pain and inflammation at the injection site is also common for parenterally administered benzathine benzylpenicillin, benzylpenicillin, and, to a lesser extent, procaine benzylpenicillin. Although penicillin is still the most commonly reported allergy, less than 20% of people who believe that they have a penicillin allergy are truly allergic to penicillin; nevertheless, penicillin is still the most common cause of severe allergic drug reactions. Significantly, there is an immunologic reaction to Streptolysin S, a toxin released by certain killed bacteria and associated with Penicillin injection, that can cause fatal cardiac syncope (Halpern et al., 2008).
Allergic reactions to any β-lactam antibiotic may occur in up to 1% of patients receiving that agent. The allergic reaction is a Type I hypersensitivity reaction. Anaphylaxis will occur in approximately 0.01% of patients. It has previously been accepted that there was up to a 10% cross-sensitivity between penicillin-derivatives, cephalosporins, and carbapenems, due to the sharing of the β-lactam ring. Assessments in 2006 found no more risk for cross-allergy for second-generation or later cephalosporins than the first generation. However, as a general risk, research shows that all beta lactams have the intrinsic hazard of very serious hazardous reactions in susceptible patients. Only the frequency of these reactions vary, based on the structure. A major feature in determining frequency of immunological reactions is the similarity of the side chains (e.g., first generation cephalosporins are similar to penicillins); this is why the β-lactams are associated with different frequencies of serious reactions (e.g., anaphylaxis) (Pichichero, 2007).
Glutathione (GSH)
Glutathione (GSH) is an important antioxidant in plants, animals, fungi, and some bacteria and archaea, preventing damage to important cellular components caused by reactive oxygen species such as free radicals, peroxides, lipid peroxides and heavy metals. It is a tripeptide with a gamma peptide linkage between the carboxyl group of the glutamate side-chain and the amine group of cysteine (which is attached by normal peptide linkage to a glycine) (Pompella, et al., 2013). Glutathione reduces disulfide bonds formed within cytoplasmic proteins to cysteines by serving as an electron donor. In the process, glutathione is converted to its oxidized form, glutathione disulfide (GSSG), also called L-(–)-glutathione.
Once oxidized, glutathione can be reduced back by glutathione reductase, using nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) as an electron donor. The ratio of reduced glutathione to oxidized glutathione within cells is often used as a measure of cellular toxicity. The biosynthesis pathway for glutathione is found in some bacteria, such as cyanobacteria and proteobacteria, but is missing in many other bacteria. Most eukaryotes synthesize glutathione, including humans, but some do not, such as Leguminosae, Entamoeba, and Giardia. The only archaea that make glutathione are halobacteria (Copley and Dhillon, 2012)
Glutathione is not an essential nutrient for humans, since it can be biosynthesized in the body from the amino acids L-cysteine, L-glutamic acid, and glycine. The sulfhydryl group (SH) of cysteine serves as a proton donor and is responsible for its biological activity. Cysteine is the rate-limiting factor in cellular glutathione biosynthesis, since this amino acid is relatively rare in foods.
Cells make glutathione in two adenosine triphosphate-dependent steps:
- First, gamma-glutamylcysteine is synthesized from L-glutamate and cysteine via the enzyme gamma-glutamylcysteine synthetase (glutamate cysteine ligase, GCL). This reaction is the rate-limiting step in glutathione synthesis.
- Second, glycine is added to the C-terminal of gamma-glutamylcysteine via the enzyme glutathione synthetase.
Animal glutamate cysteine ligase (GCL) is a heterodimeric enzyme composed of a catalytic and a modulatory subunit. The catalytic subunit is necessary and sufficient for all GCL enzymatic activity, whereas the modulatory subunit increases the catalytic efficiency of the enzyme. Mice lacking the catalytic subunit (i.e., lacking all de novo GSH synthesis) die before birth. Mice lacking the modulatory subunit demonstrate no obvious phenotype, but exhibit marked decrease in GSH and increased sensitivity to toxic insults (Kumar, 2011).
While all cells in the human body are capable of synthesizing glutathione, liver glutathione synthesis has been shown to be essential. Mice with genetically induced loss of GCLC (i.e., GSH synthesis) only in the liver die within a month of birth (Chen and Yang, 2007). The plant glutamate cysteine ligase (GCL) is a redox-sensitive homodimeric enzyme, conserved in the plant kingdom. In an oxidizing environment, intermolecular disulfide bridges are formed and the enzyme switches to the dimeric active state. The midpoint potential of the critical cysteine pair is -318 mV. In addition to the redox-dependent control is the plant GCL enzyme feedback inhibited by GSH. GCL is exclusively located in plastids, and glutathione synthetase is dual-targeted to plastids and cytosol, thus are GSH and gamma-glutamylcysteine exported from the plastids. Both glutathione biosynthesis enzymes are essential in plants; knock-outs of GCL and GS are lethal to embryo and seedling (Hothorn, 2006).
Functions of glutathione
Glutathione exists in both reduced (GSH) and oxidized (GSSG) states. In the reduced state, the thiol group of cysteine is able to donate a reducing equivalent (H++ e−) to other unstable molecules, such as reactive oxygen species. In donating an electron, glutathione itself becomes reactive, but readily reacts with another reactive glutathione to form glutathione disulfide (GSSG). Such a reaction is probable due to the relatively high concentration of glutathione in cells (up to 5 mM in the liver).
GSH can be regenerated from GSSG by the enzyme glutathione reductase (GSR): NADPH reduces Flavin adenine dinucleotide (FAD) present in GSR to produce a transient FADH-anion. This anion then quickly breaks a disulfide bond (Cys58 – Cys63) and leads to Cys63’s nucleophilically attacking the nearest sulfide unit in the GSSG molecule (promoted by His467), which creates a mixed disulfide bond (GS-Cys58) and a GS-anion. His467 of GSR then protonates the GS-anion to form the first GSH. Next, Cys63 nucleophilically attacks the sulfide of Cys58, releasing a GS-anion, which, in turn, picks up a solvent proton and is released from the enzyme, thereby creating the second GSH. So, for every GSSG and NADPH, two reduced GSH molecules are gained, which can again act as antioxidants scavenging reactive oxygen species in the cell.
In healthy cells and tissue, more than 90% of the total glutathione pool is in the reduced form (GSH) and less than 10% exists in the disulfide form (GSSG). An increased GSSG-to-GSH ratio is considered indicative of oxidative stress (Halprin, 2007)
Glutathione has multiple functions:
- It is the major endogenous antioxidant produced by the cells, participating directly in the neutralization of free radicals and reactive oxygen compounds, as well as maintaining exogenous antioxidants such as vitamins C and E in their reduced (active) forms.
- Regulation of the nitric oxide cycle is critical for life, but can be problematic if unregulated.
- It is used in metabolic and biochemical reactions such as deoxyribonucleic acid (DNA) synthesis and repair, protein synthesis, prostaglandin synthesis, amino acid transport, and enzyme activation. Thus, every system in the body can be affected by the state of the glutathione system, especially the immune system, the nervous system, the gastrointestinal system, and the lungs.
- It has a vital function in iron metabolism. Yeast cells depleted of or containing toxic levels of GSH show an intense iron starvation-like response and impairment of the activity of extramitochondrial enzymes, followed by death.
References
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