Navigating the tumor microenvironment: mesenchymal stem cell-mediated delivery of anticancer agents

Scientific knowledge of cancer has advanced greatly throughout the years, with most recent studies findings includes many hallmarks that capture disease's multifaceted character. One of the novel approach utilised for the delivery of anti-cancer agents includes mesenchymal stem cell mediated drug delivery. Mesenchymal stem cells (MSCs) are non-haematopoietic progenitor cells that may be extracted from bone marrow, tooth pulp, adipose tissue and placenta/umbilical cord blood dealing with adult stem cells. MSCs are mostly involved in regeneration of tissue, they have also been shown to preferentially migrate to location of several types of tumour in-vivo. Usage of MSCs ought to improve both effectiveness and safety of anti-cancer drugs by enhancing delivery efficiency of anti-cancer therapies to tumour site. Numerous researches has demonstrated that various drugs, when delivered via mesenchymal stem cell mediated delivery can elicit anti-tumour effect of cells in cancers of breast cells and thyroid cells. MSCs have minimal immunogenicity because to lack of co-stimulatory molecule expression, which means there is no requirement for immunosuppression after allogenic transplantation. This current review elaborates recent advancements of mesenchyma stem cell mediated drug delivery of anti-cancer agents along with its mechanism and previously reported studies of drugs manufactured via this drug delivery system.

Sustained release delivery of favipiravir through statistically optimized, chemically cross-linked, pH-sensitive, swellable hydrogel

In the current work, favipiravir (an antiviral drug) loaded pH-responsive polymeric hydrogels were developed by the free redical polymerization technique. Box-Behnken design method via Design Expert version 11 was employed to furnish the composition of all hydrogel formulations. Here, polyethylene glycol (PEG) has been utilized as a polymer, acrylic acid (AA) as a monomer, and potassium persulfate (KPS) and methylene-bisacrylamide (MBA) as initiator and cross-linker, respectively. All networks were evaluated for in-vitro drug release (%), sol-gel fraction (%), swelling studies (%), porosity (%), percentage entrapment efficiency, and chemical compatibilities. According to findings, the swelling was pH sensitive and was shown to be greatest at a pH of 6.8 (2500%). The optimum gel fraction offered was 97.8%. A sufficient porosity allows the hydrogel to load a substantial amount of favipiravir despite its hydrophobic behavior. Hydrogels exhibited maximum entrapment efficiency of favipiravir upto 98%. The in-vitro release studies of drug-formulated hydrogel revealed that the drug release from hydrogel was between 85 to 110% within 24 h. Drug-release kinetic results showed that the Korsmeyer Peppas model was followed by most of the developed formulations based on the R2 value. In conclusion, the hydrogel-based technology proved to be an excellent option for creating the sustained-release dosage form of the antiviral drug favipiravir.

Advanced polymers and recent advancements on gastroretentive drug delivery system; a comprehensive review

Oral route of drug administration is typically the initial option for drug administration because it is both practical and affordable. However, major drawback of this route includes the release of drug at a specified place thus reduces the bioavailability. This could be overcome by utilising the gastroretentive drug delivery system (GRRDS). Prolonged stomach retention improves bioavailability and increases solubility for medicines that are unable to dissolve in high pH environments. Many recent advancements in the floating, bio adhesive, magnetic, expandable, raft forming and ion exchange systems have been made that had led towards advanced form of drug delivery. From the past few years, floating drug delivery system has been most commonly utilised for the delivery of drug in a delayed manner. Various polymers have been utilised for manufacturing of these systems, including alginates, chitosan, pectin, carrageenan's, xanthan gum, hydroxypropyl cellulose, carbomer, polyethylene oxide and sodium carboxy methyl cellulose. Chitosan, pectin and xanthan gum have been found to be most commonly used polymers in the manufacturing of drug inclusion complex for gastroretentive drug delivery. This study aimed to define various types and advanced polymers as well as also highlights recent advances and future perspectives of gastroretentive drug delivery system.

A comprehensive review on transethosomes as a novel vesicular approach for drug delivery through transdermal route

Drug delivery through transdermal route is one of the effective methods for the application of drugs. It overcomes many drawbacks which are encountered with the oral route. Moreover, many drugs are not able to pass through the stratum corneum, which is the main barrier for the transdermal drug delivery. Formation of ultra-deformable vesicles (UDVs) is a novel technique for the transdermal applications of the drugs. Transethosomes (TEs), ethosomes, and transferosomes are all part of the UDV. Because of the presence of increased concentrations of ethanol, phospholipids, and edge activators, TEs provide improved drug permeation through the stratum corneum. Because of the elasticity of TEs, drug penetration into the deeper layer of skin also increases. TEs can be prepared using a variety of techniques, including the cold method, hot method, thin film hydration method, and the ethanol injection method. It increases patient adherence and compliance because it is a non-invasive procedure of administering drugs. Characterization of the TEs includes pH determination, size and shape, zeta potential, particle size determination, transition temperature, drug content, vesicle stability, and skin permeation studies. These vesicular systems can be utilized to deliver a variety of medications transdermally, including analgesics, antibiotics, antivirals, and anticancer and arthritis medications. This review aims to describe vesicular approaches that had been used to overcome the barrier for the transdermal delivery of drug and also describes brief composition, method of preparation, characterization tests, mechanism of penetration of TEs, as well as highlighted various applications of TEs in medicine.

Formulation and evaluation of miconazole lipogel for enhanced drug permeation

Hydrophilic drugs could be incorporated into the skin surface by manes of Lipogel. This study aimed to prepare miconazole lipogel with natural ingredients to enhance drug permeability using dimethyl Sulfoxide (DMSO). The miconazole lipogels, A1 (without DMSO) and A2 (with DMSO) were formulated and evaluated for organoleptic evaluation, pH, viscosity, stability studies, freeze-thawing, drug release profile and drug permeation enhancement. Results had stated that prepared lipogel's pH falls within the acceptable range required for topical delivery (4 to 6) while both formulations show good results in organoleptic evaluation. The A2 formulation containing DMSO shows better permeation of miconazole (84.76%) on the artificial skin membrane as compared to A1 lipogel formulation (50.64%). In in-vitro drug release studies, A2 for-mulation showed 87.48% drug release while A1 showed just 60.1% drug release from lipogel. Stability studies were performed on model formulations under environmental conditions and both showed good spreadibility, stable pH, free of grittiness and good consistency in formulation. The results concluded that A2 formulation containing DMSO shows better results as compared to DMSO-free drug lipogel.

Formulation of Aloe vera based curcumin topical gel and its in-vitro evaluation

Curcumin is a polyphenolic compound obtained from the rhizome of plant. Curcuma longa possesses antioxidant, anti-inflammatory and wound-healing properties. The current study was designed to formulate an Aloe vera-based curcumin topical gel. To enhance curcumin's solubility, it was first complexed with β-cyclodextrin, given its hydrophobic nature. While Carbopol, carboxy methyl cellulose and guar gum were used in various concentrations as gelling agents for preparation of the formulations. The effect of propylene glycol as a permeation enhancer was also observed. The prepared formulations were tested for different parameters such as physical appearance, spreadability, drug content, pH, viscosity and in-vitro permeation. All the formulations were found to be stable. All formulations consisting of propylene glycol showed permeation within the range of 80-90%. The maximum percentage of drug release was observed in the formulation containing 1% Carbopol 940 as the gelling agent which also exhibited good spreadability. In comparison to gels formulated with carboxymethyl cellulose and guar gum, Carbopol 940 gels appeared more translucent. Consequently, it was concluded that curcumin's permeation improved following its complexation with β-cyclodextrin. This complex when further used for the formation of an aloe vera based topical gel with 1% Carbopol 940 and 10% propylene glycol demonstrated maximum efficacy.

Vesicular approach of cubosomes, its components, preparation techniques, evaluation and their appraisal for targeting cancer cells

Cancer has been characterized by abnormal and uncontrolled proliferation of cells. Majority of drugs given through chemotherapy produce unwanted and adverse effects of chemotherapeutic agents to the other healthy cells and tissues of body. Various nanocarriers have now been considered for treatment of cancer. Among various nanocarriers, cubosomes are the nano sized dispersions that have drawn interest of researchers recently. Cubosomes are defined as dispersions of colloidal nature containing cubic crystalline liquid formations in aqueous medium in presence of suitable surfactant molecules. The unique capacity to encapsulate lipophilic, hydrophilic, and amphiphilic compounds inside their structure distinguishes them among others. Top- down method and hydrotrope method are most often employed methods for cubosomes preparation. Cubosomes can be characterized by Polarized light microscopy Photon correlation spectroscopy X-ray scattering (SAXS), Transmission electron microscopy and various stability studies. Cubic lipid nanoparticles have a very stable cubic structure that enables slower dissociation rate, increased retention and site-specific delivery of drugs. Cubosomes containing extracts of cornelian cherry for boosting anti-cancerous effects in cancer of colorectal cells by preventing against GIT destruction. When applied for skin cancer, cubosomes have shown to be having enhanced permeation of the drug. In liver cancer, increased bioavailability of drug was observed via cubosomes. This current review elaborates the advancement of cubosomes and their effective role in the treatment of cancer. This review aims to describe vesicular approach of cubosomes, its composition and method of preparation, characterization tests as well as elaborates various applications of cubosomes in cancer.

Solid lipid nanoparticles: a versatile approach for controlled release and targeted drug delivery

Solid Lipid Nanoparticles (SLN), the first type of lipid-based solid carrier systems in the nanometer range, were introduced as a replacement for liposomes. SLN are aqueous colloidal dispersions with solid biodegradable lipids as their matrix. SLN is produced using processes like solvent diffusion method and high-pressure homogenization, among others. Major benefits include regulated release, increased bioavailability, preservation of peptides and chemically labile compounds like retinol against degradation, cost-effective excipients, better drug integration, and a broad range of applications. Solid lipid nanoparticles can be administered via different routes, such as oral, parenteral, pulmonary, etc. SLN can be prepared by using high shear mixing as well as low shear mixing. The next generation of solid lipids, nanostructured lipid carriers (NLC), can reduce some of the drawbacks of SLN, such as its restricted capacity for drug loading and drug expulsion during storage. NLC are controlled nanostructured lipid particles that enhance drug loading. This review covers a brief introduction of solid lipid nanoparticles, manufacturing techniques, benefits, limitations, and their characterization tests.

Role of vitamins B6, B12 and folic acid on hyperhomocysteinemia in a Pakistani population of patients with acute myocardial infarction

BACKGROUND AND AIM

Pakistani people belong to an ethnic group which has the highest rate of coronary artery disease (CAD). We investigated the possible correlation between deficiency of vitamins B6, B12 or folic acid and hyperhomocysteinemia in Pakistani patients with acute myocardial infarction (AMI). A case-control study was carried out involving 224 AMI patients (age 30-70 years; 55 females and 169 males) and 126 normal healthy subjects (age 31-70 years; 35 females and 91 males).

METHODS AND RESULTS

Fasting venous blood was obtained from cases and controls. Serum was analyzed for folic acid and B12 using radioassays. Plasma was analyzed for pyridoxal phosphate (PLP; coenzymic form of B6) using a radioenzymatic assay and for total homocysteine using a fluorescence polarization immunoassay. Mean serum B12 concentration in AMI patients was found to be significantly lower than the mean for controls (241+/-185 pg/ml vs 608+/-341 pg/ml; p < 0.001). Mean serum folate level in patients was also found to be lower than controls (3.35+/-3.78 ng/ml vs 4.93+/-2.93 ng/ml), however, the differences were not statistically significant. Similarly, mean PLP concentration in plasma of cases (19.4+/-24.4 nmol/l) was lower than the concentration in controls (23.2+/-17.6 nmol/l), but the difference was not statistically significant. Mean plasma homocysteine level in AMI cases (18+/-8.36 micromol/l) was higher than the mean level in controls (16.4+/-4.9 micromol/l), but not to a significant extent. However, this mean homocysteine concentration in normal healthy subjects was among the highest reported in the literature and was significantly more than mean values reported in most Eastern and Western studies. Compared to controls, there was significantly greater deficiency of folate (32.5% vs 67.1%), B12 (3.2% vs 63.4%) and PLP (49.2% vs 74.1%) in AMI patients. Deficiencies of folate, B12 and PLP were defined as serum folate levels less than 3.5 ng/ml, serum levels of B12 less than 200 pg/ml and plasma PLP levels less than 20 nmol/l. Mean plasma homocysteine levels in smokers were found to be significantly higher in both cases and controls. Similarly, mean serum folate levels in smokers (compared to nonsmokers) were significantly lower in both cases and controls.

CONCLUSIONS

Substantial nutritional deficiencies of these three vitamins along with mild hyperhomocysteinemia, perhaps through an interplay with the classical cardiovascular risk factors (highly prevalent in this population), could be further aggravating the risk of CAD in the Pakistani population.

Determination of alpha-1 antitrypsin genetic deficiency in duodenal ulcer by polymerase chain reaction

OBJECTIVE

To confirm alpha-1-AT deficiency status in duodenal ulcer using a combination of PCR and restricted enzyme digestion.

METHODS

Fifty patients with endoscopically proven duodenal ulcer and hundred controls with no signs of the disease were included. Alpha-1-AT phenotypes were confirmed by polymerase chain reaction followed by restriction enzyme digestion.

RESULTS

Alpha-1-AT concentration in duodenal ulcer patients showed a mean value of 2.12 +/- 0.11 g/l (range: 0.52-3.95 g/l, p < 0.05). In controls this was 2.47 +/- 0.08 g/l (range: 0.52-5.0 g/l). Among the controls 70% had the MM phenotype, 28% M1 M2 and 2% FM. In duodenal ulcer, MM predominates (70%), followed by M1 M2 (18%), SS (4%), SZ (4%), ZZ (2%) and MZ (2%).

CONCLUSION

Alpha-1 AT deficiency was found in 10% of duodenal ulcer patients. DNA analysis more accurately resolved the phenotypes as S and Z mutations.

Down's syndrome: prospects for prevention by antenatal diagnosis

The results of a prospective study on cytogenetic analysis of Chorionic Villus Samples (CVS) taken in early pregnancy (after 10 weeks) from pregnant ladies aged between 22 and 50 years are being presented.

OBJECTIVE

To find out the prevalence of chromosomal defects with advancing age of the mother.

SETTING

Department of Medical Genetics, Armed Forces Institute of Pathology, Rawalpindi.

METHODS

A total of 48 samples have been studied. Ten patients were above the age of 35 years and 38 were below the age of 35 years. Chorionic villus samples were obtained after 10th week of pregnancy through transabdominal approach. Cytogenetic cultures were set up both by the direct and routine methods.

RESULTS

Three out of the seven samples taken from expecting mothers aged above 35 and one culture from a patient aged less than 35, showed trisomy 21.

CONCLUSION

This study highlights the fact that incidence of chromosomal aberrations and the Down's syndrome in particular, increases with the advancing maternal age. Prenatal studies can therefore be utilized to decrease the incidence of various chromosomal abnormalities.

Proteins in renal stones and urine of stone formers

Knowledge of the essential characteristics of macromolecules constituting the organic matrix of the nidus of urinary stones is required to understand the mechanism of urolithogenesis. The aim of this study was to isolate and characterise those stone nidus proteins. Using an extraction buffer containing SDS and beta-mercaptoethanol, we were able to overcome known problems of protein isolation from urinary stone matrix. These proteins were characterised by a strong tendency to aggregate under reducing and denaturing conditions. On SDS-PAGE, their molecular weights range from < or = 12 to 66 kDa. Antisera raised against stone matrix proteins showed a cross-reactivity between proteins isolated from different stones irrespective of their origin or mineral composition. Moreover, urinary proteins from stone formers also cross-reacted with these whereas there was no reaction with urinary proteins of non-stone formers. Western blotting confirmed these findings. Given the above summarised properties, it can be safely concluded that these proteins are prevalent in urines of stone formers, that they are selectively incorporated into renal stones of all aetiologies, and that they most likely have a role in nidus and, therefore, early stone formation.

Urinary N-acetyl-beta-D-glucosaminidase in rheumatoid arthritis

Excretion of urinary N-acetyl beta-D-glucosaminidase (NAG) and its isoenzyme patterns were studied in two groups of patients with rheumatoid arthritis (RA) and in normal control subjects. Urine samples were collected from 30 seropositive RA patients, 19 seronegative RA patients, and 15 normal healthy subjects. All the patients and normal subjects were assessed to have normal liver and kidney functions. A small portion of the urine sample was dialyzed against 0.01 M phosphate buffer, pH 7.0 and NAG activity was monitored. Mean +/- SD values of urinary NAG in seropositive RA patients, in seronegative RA patients and in normal healthy subjects were found to be 4.20 +/- 3.73 U/g creatinine, 2.96 +/- 2.11 U/gm creatinine, and 1.71 +/- 0.6 U/g creatinine, respectively. The mean urinary, NAG value in RA patients was found to be significantly higher (P < 0.05) in seropositive RA compared to the mean NAG value in normal healthy subjects and patients with seronegative RA when analyzed by one way ANOVA and Tukey-HSD test. The mean proportion of isoenzyme form B to isoenzyme form A in seropositive RA patients was also found to be significantly different (P < 0.05) from the mean proportion of these forms in normal healthy subjects and seronegative RA patients. There also appears to be a correlation between the concentration of urinary NAG and severity of the disease in seropositive RA.

Genetic markers and duodenal ulcer

Serum pepsinogen, alpha 1-antitrypsin (alpha 1-AT) and blood groups were studied as genetic markers in 32 patients with endoscopically proven duodenal ulcer and 44 control subjects with no family history of ulcer disease. Serum pepsinogen was determined by the modified method of Edward et al, alpha 1-AT by single radial immunodiffusion (RID) and phenotyping was carried out by isoelectric focusing (IEF). Duodenal ulcer patients with hyper- pepsinogenemia (28%) and low serum alpha 1-AT (35%) had a dominant blood group O, lower mean age, an early onset of disease, a higher frequency of gastrointestinal (GI) bleeding and ulcer perforation. These parameters were found considerably different in patients with normal serum pepsinogen and alpha 1-AT. Phenotype analysis of alpha 1-AT revealed that four duodenal ulcer patients had partial deficiency of the protease inhibitor and none of the normal exhibited the deficiency pattern. The etiology of the disease appears to be genetic anomaly in 28% of patients while the rest (72%) had ulcers as a result of neuroendocrinological or environmental factors.

Serum alpha 1 antitrypsin and pulmonary emphysema

Using isoelectric focusing (IEF) and radial immunodiffusion (RID) techniques, serum samples from 100 normal healthy adults and 21 patients with pulmonary emphysema were analysed to identify various alpha 1 antitrypsin phenotypes and the serum concentrations. Ten percent of the patients had low serum values. The normal or most common genetic form, MM, is the predominant phenotype in both controls and patients.

Inhibition studies on LDH isoenzyme purified from Uromastix testes

An LDH isoenzyme was purified to homogeneity from uromastix testes and its inhibition spectrum towards known LDH isoenzyme inhibitors studied. Platinum compounds inhibited the enzyme in the forward reaction (pyruvate-->lactate) only, n-hexanediol and colchicine showed no inhibition and gossypol acetic acid (GAA) strongly inhibited both the forward and reverse reactions and the reactions were time-dependent. Oxalate caused non-competitive inhibition (Ki app = IC50 = 0.15 mM) of the forward reaction, NADH was more effective in blocking inhibition by GAA than pyruvate. This enzyme was also unable to use ketocaproic acid as a substrate.

Genetic variants of serum alpha 1 antitrypsin

Complete absence of data on alpha 1 antitrypsin in this country prompted us to determine serum levels using radial immunodiffusion (RID) and phenotypes by isoelectric focusing (IEF) in 100 healthy adults (52 males and 48 females). Mean serum alpha 1 antitrypsin concentration in healthy subjects was 2.47 +/- 0.08 g/l and the main phenotypes MM (70%), M1 M2 (28%) and FM 3 (2%) are infrequent in our population.

Purification and properties of lactate dehydrogenase from liver of Uromastix hardwickii

Lactate dehydrogenase isoenzyme-1 was purified from liver of Uromastix hardwickii using colchicine-Sepharose and heat-inactivation methods. The crude enzyme showed four isoenzymes by agarose gel electrophoresis (AGE). The purified enzyme showed a single band after native AGE and SDS-PAGE corresponding to a molecular weight of 34 kDa. The enzyme did not bind with DEAE-Sepharose at pH 7.2. The optimum pH for forward reaction was 7.5, while for reverse reaction, the maximum activity was at pH 9.5. The Km values for pyruvate, NADH, lactate and NAD+ were 0.105, 0.045, 9.0 and 0.011 mM, respectively. The pyruvate showed maximum activity at about 150 microM and then starts showing inhibition at higher concentration. Pre-heating of enzyme showed that it was stable at 80 degrees C for 30 min and at 100 degrees C it became inactive immediately. Oxalate, glutamate, Cu2+, Co2+, Mn2+, and Mg2+ have shown inhibitory effects both for forward- and reverse-reactions. From these properties, we suggest that LDH-1 from Uromastix liver may be quite different from that of other vertebrates.

The isoenzyme forms of lactate dehydrogenase from the testes of Uromastix hardwickii

Lactate dehydrogenase was purified from testes of Uromastix hardwickii. The enzyme did not bind to DEAE-Sepharose at pH 7.2. A gel electrophoretic study of the crude enzyme showed the presence of three isoenzymes. The pH optima for pyruvate reduction and lactate oxidation were 7.0 and 9.5, respectively. The purified enzyme showed a single band after SDS-PAGE corresponding to a molecular weight of 34 KDa. The Km values for pyruvate, NADH, lactate and NAD+ were 0.019, 0.045, 9.0 and 0.011 mM, respectively. Pre-heating of the enzyme showed that it was stable up to 70 degrees C.

Detection of west Nile and Japanese encephalitis viral genome sequences in cerebrospinal fluid from acute encephalitis cases in Karachi, Pakistan

Reverse transcriptase-polymerase chain reaction (RT-PCR) on 24 cerebrospinal fluid (CSF) specimens collected between February and August 1992 detected genome sequence of West Nile (WN) virus in 8 specimens and Japanese encephalitis (JE) virus in a single specimen. The results, combined with the data by IgM-ELISA on CSF indicated that a significant proportion of acute encephalitis cases in Karachi, Pakistan, were caused by WN virus infection, while JE virus caused a small fraction.

Serum alpha 1-antitrypsin and duodenal ulcer

Evaluation of serum alpha 1-antitrypsin levels in the South Asian population and its possible involvement in disease conditions such as duodenal ulcer has not been given due consideration. This is mainly because reports from European and North American countries indicate that the genetic deficiency of this protease inhibitor is rare among Asians of the subcontinent. Using isoelectric focusing (IEF) and radial immunodiffusion (RID) techniques, we analysed serum samples from 100 normal, healthy adults and 50 patients with endoscopically proven duodenal ulcers to determine if there is a possible relationship between alpha 1-antitrypsin phenotype and this disease. Five duodenal ulcer patients had low alpha 1-antitrypsin levels as well as SZ and S phenotype. None of the controls showed presence of S or SZ phenotypes. The normal or most common genetic form, MM, is the predominant phenotype in both controls and patients.

Estimation and separation of N-acetyl-beta-D-glucosaminidase isoenzymes in urine

N-acetyl-beta-D-glucosaminidase is a lysosomal enzyme made up of two isoenzymes (A and B). It has been used extensively as a marker for kidney damage. However, its estimation in urine has not been standardized. We have established a method for the estimation and separation of NAG isoenzymes by ion-exchange chromatography. In 19 experiments done so far, this method has given reproducible results. The significance of this method is that with a single experiment, one can estimate total as well as individual isoenzyme activity. Furthermore, urine constituents do not appear to interfere in this assay.

Heterogeneity of methotrexate binding in human colon tumor cells

[3H]-methotrexate binding at pH 5.0 and pH 7.2 by the cytosol of tumor tissues and the surrounding normal areas of the gastrointestinal tract of patients suffering from colon or gastric cancer has been used to identify in these cells the presence of a binder of methotrexate having low-affinity for this drug in addition to the enzyme dihydrofolate reductase. Scatchard analysis of the [3H]-methotrexate binding data by a colon tumor sample also reveals that there are two binders of this drug present in the cytosol of these cells. The association constant (Kass) for one binder of methotrexate is = 5.6 x 10(7) M-1 while the Kass for the second binder is = 1.0 x 10(6) M-1. The two binders do not differ very much in their apparent molecular weight. Upon isoelectric focusing, the tumor cell cytosol resolves into 4 major isoproteins each having the ability not only to bind [3H]-methotrexate but also reduce [3H]-pteroylglutamic acid to [3H]-tetrahydropteroylglutamic acid. This suggests that the two binders of methotrexate may be the two forms of dihydrofolate reductase having different affinities for this anticancer drug.

Phosphate uptake by primary renal proximal tubule cell cultures grown in hormonally defined medium

The uptake of labeled inorganic phosphate into primary rabbit kidney proximal tubule cells has been examined. Phosphate was accumulated into the primary proximal tubule cells against a concentration gradient. This accumulation was sensitive to inhibition by metabolic inhibitors. The dependence of phosphate uptake on the extracellular phosphate concentration was examined. Similarities were observed between primary proximal tubule cells and the LLC-PK1 cell line in these regards. These phosphate uptake data were then plotted on a Lineweaver-Burke plot. A nonlinear plot was obtained, which suggested that phosphate uptake occurs by means of a Na+ dependent, carrier mediated process, as well as by another Na+ independent mechanism. The pH dependence of phosphate uptake was also examined. Unlike previous observations with LLC-PK1 cells, optimal phosphate uptake occurred at pH 6.5. However, this difference between the two cell culture systems may possibly be explained by differences in uptake conditions. The dependence of phosphate uptake on the extracellular NaCl concentration was examined at three different pH values. The rate of phosphate uptake at pH 7.0 was observed to saturate at a lower NaCl concentration than at either pH 6.0 or pH 6.5. Furthermore, the optimal rate of phosphate uptake at pH 7.0 was observed to be higher than at the other two pH values studied when the NaCl concentration was below 120 mM. However, when the NaCl concentration was raised to 150 mM, optimal phosphate was observed to occur at pH 6.5 rather than at pH 7.0. These observations may be explained if the pH affects not only the rate of phosphate uptake but also the affinity of the phosphate uptake system for sodium. Phosphate uptake was also observed to be sensitive to several agents, Na2 X SO4 and NaSCN, which affect the membrane potential. As observed with phosphate uptake by LLC-PK1 (and renal brush border membrane vesicles), phosphate uptake was highly sensitive to inhibition by the phosphate analogue arsenate. Novel observations were that the phosphate analogue vanadate and its cellular metabolite vanadyl stimulated the initial rate of phosphate uptake.

Effects of 2',3'-dideoxynucleosides on mammalian cells and viruses

Previous studies on the biological effects of the 2',3'-dideoxynucleosides (ddNs) have shown that while ddAdo is lethal to E. coli, ddThd has minimal effects on the growth of mammalian cell lines and that it inhibits retrovirus infection of some cell lines but not others. Previous studies have also shown that the 5'-triphosphate of ddThd, ddTTP, selectively inhibits cellular DNA polymerases beta and gamma and retroviral reverse transcriptases. Cellular DNA polymerase alpha is relatively resistant to ddTTP. We have extended these findings to show that the 5'-triphosphates of the other 3 ddNs (ddATP, ddCTP, and ddGTP) affect cellular DNA polymerases alpha, beta, and gamma in the same fashion as does ddTTP. We also show that all four ddNs in concentrations up to 100 microM have negligible effects on the growth of NIH Swiss 3T3 cells. These negligible effects may be due to inefficient intracellular phosphorylation of each nucleoside to the triphosphate. We have determined that, in several different cell lines, ddThd is phosphorylated only at a very slow rate to ddTTP, and in the one cell line tested (monkey CV-1 cells), ddAdo and ddGuo are also poorly phosphorylated. Both ddAdo and ddGuo, and probably ddThd, are converted by CV-1 cells to additional unknown compounds which may have biological activity. The four ddNs display effects of different magnitudes on certain virus infections. Although 30 microM ddThd inhibits herpes simplex I infection of CV-1 cells by 50%, 30 microM ddAdo has no effect. Infection of NIH Swiss 3T3 cells by 334C murine leukemia virus is inhibited 70-80% by ddAdo, ddCyd, and ddThd at 50 microM, but inhibition by 50 microM ddGuo is 100%.

In vitro DNA synthesis by an alpha-like DNA polymerase bound to replicating simian virus 40 chromosomes

Simian virus 40 chromosomes carry out replicative DNA synthesis in vitro which is sensitive to aphidicolin and to N-ethylmaleimide, resistant to 2',3'-dideoxythymidine-5'-triphosphate, and proportional to the amount of chromosome-associated alpha-like polymerase. Thus, an alpha-like DNA polymerase (alpha polymerase or delta polymerase) is responsible for in vitro DNA synthesis.

Both parental deoxyribonucleic acid strands at each replication fork of replicating simian virus 40 chromosomes are cut by a single-strand-specific endonuclease

We have measured the relative accessibility to a single-strand-specific endonuclease of the single-stranded DNA on the leading and lagging sides of replication forks in replicating simian virus 40 (SV40) chromosomes. To do this we have digested replicating SV40 chromosomes with a single-strand-specific endonuclease (P1 nuclease) and then characterized the intermediate and final products of digestion by sucrose gradient sedimentation and agarose gel electrophoresis. P1 nuclease rapidly and specifically cleaves parental DNA strands at replication forks, yielding intermediate and final cleavage products which are consistent with an approximately equal rate of nuclease cleavage on both sides of the fork. Thus, single-stranded DNA is approximately as accessible to P1 nuclease on the leading side of the fork as on the lagging side; the simplest interpretation of this observation is that the stretch of single-stranded DNA on the leading side is as long as that on the lagging side.