Cephaloridine cells

Although most /3- lactam antibiotics bind covalently to some or all of the same six proteins, there are decided differences among them in terms of their relative affinities. For example, cefoxitin (see Table 1 for structures) fails to bind to protein 2 while cephacetrile binds very slowly to proteins 5 and 6. Cephaloridine binds most avidly to protein 1, the transpeptidase, and inhibits cell elongation and causes lysis at its minimum inhibitory concentration. On the other hand, cephalexin binds preferentially to protein 3 and causes inhibition of cell division and filament formation (75PNA2999, 77MI51002). 

These transporters can be responsible for the toxicity of some xenobiotics. For example, the drug cephaloridine is toxic to the kidney as a result of accumulation in the proximal tubular cells, which form the cortex of the kidney. The drug is a substrate for OAT-1 on the basolateral surface and hence is transported into the proximal tubular cells. However, the transport out of these cells from the apical surface into the lumen of the tubule is restricted, probably because of the cationic group on the molecule (Fig. 7.34). The toxicity of cephaloridine is modulated by chemicals that inhibit the OAT-1 and cation transporters. The similar drug cephalothin is not concentrated in the cells and is not nephrotoxic (Table 3.5). See chapter 7 for more details. 

Active transport of compounds by the tubular cells. Compounds that are actively transported from the blood into the tubular fluid may accumulate in the proximal tubular cells, especially at concentrations where saturation of the transport system occurs. Again, concentrations to which tubular cells are exposed may be very much higher than in the bloodstream. An example of this is the drug cephaloridine, which causes proximal tubular damage as discussed in more detail in chapter 7. 

Cephaloridine is actively taken up from the blood into proximal tubular cells by the OAT 1 (Fig. 7.35). This requires a hydrophobic region as well as an anionic group, is specifically... 

Figure 7.35 The uptake and elimination of cephaloridine by proximal tubular cells in the kidney and possible mechanisms of toxicity. The uptake can be inhibited (probenicid) and the elimination also inhibited (mepiphenidol). Abbreviations OAT 1, organic anion transporter OCT, organic cation transporter ROS, reactive oxygen species.

These drugs (e.g., cephaloridine) may be nephrotoxic causing proximal tubular necrosis. Cephaloridine is actively taken up from blood into proximal tubular cells by OAT 1. The drug therefore accumulates in the kidney. Metabolic activation via cytochrome P-450 may be involved. GSH is oxidized, and as NADPH is also depleted, the GSSG cannot be reduced back to GSH. As vitamin E-depleted animals are more susceptible, it has been suggested that lipid peroxidation may be involved. Damage to mitochondria also occurs. 

The type Ilia /3-lactamase [141] can be mobilised on the R factor RPl [142] into strains of Ps. aeruginosa. The crypticity of the type Ilia /3-lactamase can then be determined against a number of substrates. That an efficient penetration barrier exists in these organisms between the substrate located outside the cell and the /8-lactamase located in the periplasmic space [141] can be seen from the following crypticity values for Ps. aeruginosa (1822 RPl) penicillin G, 80 ampicillin, 60 carbenicil-lin, 60 cephaloridine, 50. 

Because the jS-lactamase concerned is, in this instance, carried by an extrachromosomal element, it is possible to obtain R variants of the lactamase-producing strain. The availability of the R variants allows the effect of /3-lactamase production on the resistance of the pseudomonas strains to be studied directly. Table 7.8 compares single-cell resistance values obtained with R and R variants of a strain of Ps. aeruginosa. The presence of the enzyme (expressed in the R strain at a level of 3 units/mg dry wt. bacteria) increases the resistance more than 100-fold in the case of carbenicillin and penicillin G, and more than 10-fold for cephaloridine and ampicillin. 

Kiyomiya K, Matsushita N, Matsuo S, and Kurebe M. Roles of oxygen radical production and lipid peroxidation in the cytotoxicity of cephaloridine on cultured renal epithelial cells (LLC- PK1). J Vet Med Sci 62 977-981, 2000. 

Ultrastructural changes of proximal tubular cells occur as early as 1 hour after cephaloridine administration to rabbits and are characterized by loss of brush border, less elongated mitochondria and disappearance of structures associated with endocytosis. Later ultrastructural changes include disorganization of lateral interdigitations of plasma cell membrane and mitochondrial swelling [28,29]. 

The cell membrane serves as a protective barrier in renal cells. It is the initial site which p-lactams encounter in their journey to the cellular environment from the blood or tubular fluid, p-lactams may disrupt the functional organization of the membrane through peroxidation of membrane lipids, which, in turn, leads to the inability of membrane to serve as an osmotic barrier and causes the cytosol contents to leak. As a result of the cephalosporins disruptive effect on cell membrane, increased leakage of the cytosolic enzyme lactate dehydrogenase (LDH) occurs. The increased LDH concentration was from the cytosol of the renal cortex [49,71] or from isolated proximal and distal tubular cells [39] or in the urine of experimental animals [39]. The results of these studies indicate that plasma membrane became permeable to large molecules such as LDH. After cephalosporin treatment, cephaloridine caused the greatest decrease of LDH concentration in cytosol [49]. Whereas, cephaloridine induced a greater release of LDH from proximal tubular cells than cepha-lothin and cephalexin, distal cells were not affected by any of these cephalosporins [38,39]. 

Kidneys are able to carry out extensive oxidation, reduction hydrolysis and conjugation reactions. The attractive hypothesis that cephaloridine is metabolized prior to producing nephrotoxicity [92] was not substantiated by experimental data. However, pretreatment of rats with 60 mg/kg cobalt chloride decreased cephaloridine-induced lipid peroxidation in renal cortical slices [31]. These results suggest that prior to producing nephrotoxicity, cephaloridine is taken up into renal cells, where, with the involvement of cytochrome P-450, it induces peroxidation of cell membrane lipids. 

It has been shown that the renal bioactivation of xenobiotics such as the herbicides paraquat and diquat [10, 111, 112], and of p-lactams such as cephaloridine and cefsulodin [10, 40, 41] or the antitumor agent adriamycin [113, 114] can induce the generation of reactive oxygen species (oxidative stress) which can be involved in alterations of the structure and functions of cell membranes, cytoskeletal injury, mutagenicity, carcinogenicity, and cell necrosis [115-117]. 

Exposure of renal cortical microsomes or primary renal epithelial culture cells to different type of antibiotics led to a significant increase in production of superoxide and MDA after cephaloridine and mezlocillin [10, 40] but not after gentamicin [40,122]. 

For the zwitterion cephaloridine (CPH) a quantitative correlation between CPH-concentration and the degree of nephrotoxicity has been found [126]. CPH is taken up from blood into the proximal tubule cells and it was assumed that CPH uptake across the basolateral membrane occurs by the transport systems for PAH [127, 128]. However, it was also shown that zwitterionic p-lactams such as CPH can interact with... 

---