Validation of a rat pheochromocytoma (PC12)-based cell survival assay for determining biological potency of recombinant human nerve growth factor

A method has been validated, according to the Guidelines of the International Conference on Harmonization (ICH), for precise quantitation of the biological activity of recombinant human nerve growth factor (rhNGF) for lot release testing. The assay is based on the survival of a subclone of rat pheochromocytoma PC12 cells (PC12-CF) in response to rhNGF. Cell survival is measured by monitoring the reduction, by living cells, of the alamarBlue dye into a red form which is highly fluorescent. The assay is simple, has high throughput (performed in 96-well microtiter plates) and shows reproducible dose-response curves in the concentration range of 0.2-50 ng/ml. The method was validated for its linearity, accuracy, precision, robustness, and to meet current regulatory requirements. The assay demonstrated good linearity, yielding a coefficient of determination of 0.9902. Sample recovery studies demonstrated an accuracy ranging from 96 to 98%. The repeatability of the assay and intermediate precision had coefficients of variation (CV) of <9%. The assay was stability-indicating since it was able to detect changes in rhNGF samples degraded by protease treatment and in a number of isolated rhNGF variants. Robustness was demonstrated by the relative insensitivity of the assay to small deliberate changes in key method parameters. The validation data, provided in this manuscript, indicate that the newly described bioassay for rhNGF is robust, accurate, precise, and suitable for lot release potency testing of rhNGF.

A cell-based potency assay for insulin-like growth factor-I

The authors developed a cell-based bioassay for determining the potency of recombinant human insulin-like growth factor I (IGF-I) using HU-3 human megakaryoblastic cell line. Cell proliferation was measured using the alamarBlue fluorescence method. The addition of IGF-I resulted in a dose-dependent growth response after 48 hours under serum-free conditions. The effective range was 0.1-25 ng/ml with half-maximal response at approximately 2 ng/ml IGF-I. The assay is simple, requiring just three steps, performed in 96-well microtitre plates and is able to detect changes in activity of truncated analogues of IGF-I (such as des-Gly-IGF-I, des-Gly-Pro-IGF-I and des-Gly-Pro-Glu-IGF-I) as well as IGF-I samples that had been subjected to proteolytic or disulfide reduction treatments. This assay is precise, with interassay variability of less than 10% and accurate, with percentage recoveries of nearly 100%. The relative efficacies of other insulin-related peptides in stimulating cell growth of the cell line were examined. IGF-II was 5-fold less potent than IGF-I and insulin had little or no proliferative activity. In addition, the growth-promoting activity correlated well with IGF-I stimulation of glucose consumption in this system. In conclusion, the HU-3 human megakaryoblastic cell line constitutes a simple system for measuring the biological activity of recombinant IGF-I in quality control set-up. The safety, convenience and precision of the assay make it an attractive alternative to radioactive and other colorimetric methods.

Growth hormone/IGF-I and/or resistive exercise maintains myonuclear number in hindlimb unweighted muscles

In the present study of rats, we examined the role, during 2 wk of hindlimb suspension, of growth hormone/insulin-like growth factor I (GH/IGF-I) administration and/or brief bouts of resistance exercise in ameliorating the loss of myonuclei in fibers of the soleus muscle that express type I myosin heavy chain. Hindlimb suspension resulted in a significant decrease in mean soleus wet weight that was attenuated either by exercise alone or by exercise plus GH/IGF-I treatment but was not attenuated by hormonal treatment alone. Both mean myonuclear number and mean fiber cross-sectional area (CSA) of fibers expressing type I myosin heavy chain decreased after 2 wk of suspension compared with control (134 vs. 162 myonuclei/mm and 917 vs. 2,076 micron2, respectively). Neither GH/IGF-I treatment nor exercise alone affected myonuclear number or fiber CSA, but the combination of exercise and growth-factor treatment attenuated the decrease in both variables. A significant correlation was found between mean myonuclear number and mean CSA across all groups. Thus GH/IGF-I administration and brief bouts of muscle loading had an interactive effect in attenuating the loss of myonuclei induced by chronic unloading.

Apoptosis: a mechanism contributing to remodeling of skeletal muscle in response to hindlimb unweighting

The role of apoptosis in the elimination of myonuclei during hindlimb unloading-induced atrophy and the inhibition of apoptosis in the prevention of muscle atrophy were examined. The number of nuclei demonstrating double-stranded DNA fragmentation seen by terminal deoxynucleotidyl transferase (TDT) histochemical staining, an indicator of apoptosis, was significantly increased after 14 days of suspension. Double staining with TDT and antilaminin immunohistochemistry revealed that some TDT-positive nuclei were within the fiber lamina and were most likely myonuclei. The number of fibers containing morphologically abnormal nuclei was also significantly greater in suspended compared with control rats. Combined treatment with growth hormone and insulin-like growth factor I (GH/ IGF-I) and resistance exercise attenuated the increase in TDT-positive nuclei (approximately 26%, P > 0.05) and significantly decreased the number of fibers with morphologically abnormal nuclei. The data suggest that 1) "programmed nuclear death" contributes to the elimination of myonuclei and/or satellite cells from atrophying fibers, and 2) GH/IGF-I administration plus muscle loading ameliorates the apoptosis associated with hindlimb unloading.

The stability of recombinant human growth hormone in poly(lactic-co-glycolic acid) (PLGA) microspheres

PURPOSE

The development of a sustained release formulation for recombinant human growth hormone (rhGH) as well as other proteins requires that the protein be stable at physiological conditions during its in vivo lifetime. Poly(lactic-co-glycolic acid) (PLGA) microspheres may provide an excellent sustained release formulation for proteins, if protein stability can be maintained.

METHODS

rhGH was encapsulated in PLGA microspheres using a double emulsion process. Protein released from the microspheres was assessed by several chromatrographic assays, circular dichroism, and a cell-based bioassay. The rates of aggregation, oxidation, diketopiperazine formation, and deamidation were then determined for rhGH released from PLGA microspheres and rhGH in solution (control) during incubation in isotonic buffer, pH 7.4 and 37 degrees C.

RESULTS

rhGH PLGA formulations were produced with a low initial burst (< 20%) and a continuous release of rhGH for 30 days. rhGH was released initially from PLGA microspheres in its native form as measured by several assays. In isotonic buffer, pH 7.4 and 37 degrees C, the rates of rhGH oxidation, diketopiperazine formation, and deamidation in the PLGA microspheres were equivalent to the rhGH in solution, but aggregation (dimer formation) occurred at a slightly faster rate for protein released from the PLGA microspheres. This difference in aggregation rate was likely due to the high protein concentration used in the encapsulation process. The rhGH released was biologically active throughout the incubation at these conditions which are equivalent to physiological ionic strength and pH.

CONCLUSIONS

rhGH was successfully encapsulated and released in its fully bioactive form from PLGA microspheres over 30 days. The chemical degradation rates of rhGH were not affected by the PLGA microspheres, indicating that the internal environment of the microspheres was similar to the bulk solution. After administration, the microspheres should become fully hydrated in the subcutaneous space and should experience similar isotonic conditions and pH. Therefore, if a protein formulation provides stability in isotonic buffer, pH 7.4 and 37 degrees C, it should allow for a safe and efficacious sustained release dosage form in PLGA microspheres.

Long-acting growth hormones produced by conjugation with polyethylene glycol

Derivatives of human growth hormone (hGH) of increasing size were produced by reaction with the N-hydroxysuccinimide ester of polyethylene glycol-5000 (PEG5000), a 5-kDa reagent that selectively conjugates to primary amines. By adjusting the reaction conditions and purification procedure, it was possible to isolate hGH derivatives containing up to seven PEG moieties that altered the Stokes radius and thereby the effective molecular masses of the unmodified hormone from 22 to 300 kDa. Fortunately, the most reactive amines were ones that did not lie in either of the two sites important for receptor binding. Nonetheless, increasing the level of PEG modification linearly reduced the affinity of hGH for its receptor and increased the EC50 in a cell-based assay up to 1500-fold. Most of the reduction in affinity was the result of slowing the association rate for the receptor. The clearance rate of hGH in rats was inversely proportional to effective molecular weight and closely fit a filtration model. We have tested the potency of these analogs by injecting them daily or every 6 days into hypophysectomized rats and determining the effects on body and organ growth. The efficacy of these analogs was optimal for hGH conjugated with 5 eq of PEG5000, and the potency was increased by about 10-fold compared with unmodified hGH. Such PEG-hGH derivatives show promise as long-acting alternatives to daily injections of hGH. More generally these studies show that improving hormone clearance properties, even at the expense of reducing receptor binding affinity, can lead to dramatic increases in hormone efficacy.

Recombinant human insulin-like growth factor binding protein-3 (rhIGFBP-3): effects on the glycemic and growth promoting activities of rhIGF-1 in the rat

The effects of IGFBPs on IGF-1 bioactivity in vivo remain largely unknown. We have tested the ability of rhIGFBP-3, made in 293 cells or CHO cells, to affect the glycemic and anabolic activities of co-administered rhIGF-1. For glycemic studies female dw/dw rats were anesthetized, a jugular catheter inserted, basal blood samples taken and i.v. injections given of rhIGF-1 (0.25 mg/kg), rhIGFBP-3 (0.50 mg/kg), or rhIGF-1 plus rhIGFBP-3 (0.25 plus 0.50 mg/kg, respectively). The blood glucose (20 min later, as a percent of initial, mean +/- SD) reached its nadir for rhIGF-1 alone (58 +/- 5%) but was not changed by rhIGFBP-3 alone (99 +/- 4%) or rhIGF-1 plus rhIGFBP-3 (93 +/- 5%). In growth studies, young female hypophysectomized rats (90-105 g) were injected s.c. twice daily for 3-4 days, or infused s.c. for 7 days, with excipient, rhIGF-1 or rhIGF-1 plus rhIGFBP-3 at doses similar to those used in the hypoglycemia studies. Weight gain induced by rhIGF-1 was either unchanged, or enhanced, when the rhIGF-1 was delivered with rhIGFBP-3. The hypoglycemic activity of IGF-1 was greatly reduced if IGF-1 was administered bound to 293-cell rhIGFBP-3 but anabolic activity was unchanged or enhanced.

Chemical heterogeneity as a result of hydroxylamine cleavage of a fusion protein of human insulin-like growth factor I

Recombinant DNA techniques were used to biosynthesize human insulin-like growth factor I (hIGF-I) as a fusion protein wherein the fusion polypeptide is an IgG-binding moiety derived from staphylococcal protein A. This fusion protein is produced in Escherichia coli and secreted into the fermentation broth. In order to release mature recombinant-derived hIGF-I (rhIGF-I), the fusion protein is treated with hydroxylamine, which cleaves a susceptible Asn-Gly bond that has been engineered into the fusion protein gene. Reversed-phase h.p.l.c. was used to estimate the purity of the rhIGF-I preparations, especially for the quantification of the methionine sulphoxide-containing variant. It was determined that hydroxylamine cleavage of the fusion protein produced, as a side reaction, hydroxamates of the asparagine and glutamine residues in rhIGF-I. Although isoelectric focusing was effective in detecting, and reversed-phase h.p.l.c. for producing enriched fractions of the hydroxamate variants, ion-exchange chromatography was a more definitive procedure, as it allowed quantification and facile removal of these variants. The identity of the variants as hydroxamates was established by Staphylococcus aureus V8 proteinase digestion, followed by m.s., as the modification was transparent to amino acid and N-terminal sequence analyses. The biological activity of rhIGF-I was established by its ability to incorporate [3H]thymidine into the DNA of BALB/c373 cells and by a radioreceptor assay utilizing human placental membranes. Both assays demonstrate that the native, recombinant and methionine sulphoxide and hydroxamate IGF-I variants are essentially equipotent.

Evidence for triiodothyronine receptors in human endometrium and myometrium

Thyroid gland dysfunction in humans may cause various female reproductive tract disorders. Thyroid hormone action is thought to be mediated by high-affinity low-capacity receptor proteins located in the nucleus. The studies detailed in this report were undertaken to determine if uterine nuclei contain specific high-affinity receptors for thyroid hormone. Nuclei from human endometrium and myometrium were prepared by homogenization and centrifugation following routine surgical procedures. With the use of isolated nuclei, binding experiments with 125I-triiodothyronine (T3) revealed a dissociation constant of approximately 1 X 10(-9) M in both endometrium and myometrium with a maximum number of binding sites equivalent to 0.06 and 0.21 pmol/mg of DNA, respectively. The solubilized binding sites were destroyed largely by trypsin treatment. Competition experiments revealed the following relative binding affinities for these nuclear binding sites: L-T3 greater than D-T3 greater than L-thyronine greater than reverse T3. These results indicate the presence in the human uterus of specific high-affinity binding sites with characteristics expected of a T3 receptor and thus raise the possibility that thyroid hormone may exert effects on the uterus through these receptors.

Relative sensitivity of the corpus luteum of different days of pregnancy to LH-deprivation in the rat and hamster

Deprivation of endogenous LH by LH antiserum (LH A/S) in 6-day pregnant rats did not affect the luteal or serum progesterone within 24 h. LH A/S treatment on day 7 or 8 of pregnancy, however, caused a 70 and 92% reduction in luteal progesterone, respectively, within 24 h. Serum levels of progesterone showed a similar reduction. In the case of pregnant hamster, unlike the rat, there was a significant decrease in progesterone in the serum, luteal and non-luteal compartments whether the A/S was administered on day 4, 5 or 6. There was more than a 10-fold increase in the luteal cholesterol esters within 24 h whether the A/S was given on day 6, 7 or 8 of pregnancy in the rat. Rat corpora lutea of days 6 and 8 of pregnancy reacted in a like manner to LH-deprivation, showing an increased utilization of [U-14C]glucose to form 14CO2 in vitro. In the rat, LH (25 mug NIH-S19) administration in vivo either on day 6 or day 8 of pregnancy, caused within 2 h an increase in serum and non-luteal progesterone, but luteal progesterone was unchanged. On the other hand, LH administration to hamsters on day 8 of pregnancy caused an increase in progesterone levels in serum, luteal and non-luteal tissue. Incubation of corpora lutea isolated from untreated 6- and 8-day pregnant rats with LH brought about an increase in progesterone secretion into the medium in both cases. The results show that, even though LH-deprivation does not apparently affect progesterone concentration in the corpus luteum of 6-day pregnant rats, it does affect other metabolic parameters such as glucose utilization and cholesterol turnover, suggesting that the corpus luteum of early pregnancy exhibits a continuous dependency on LH for the maintainence of metabolic functions.

Studies on luteolysis: effect of antiserum to luteinizing hormone on sterols and steroid levels in pregnant hamsters

The effect of luteinizing hormone antiserum (LH A/S) on sterol and steroid levels in luteal and non-luteal ovarian compartments, and on serum steroid levels of pregnant hamsters, was studied. Injection (ip) of 0.1 ml of LH A/S on day 7 caused termination of pregnancy and morphological regression of the corpus luteum (CL) within 18-20 h of treatment, whereas LH-free non-immune serum had no effect. Within 3 h of administration of LH A/S the luteal progesterone levels fell from a control value of 36.0 +/- 2.4 to 15.6 +/- 3.4 ng/mg, and estrogen from a control value of 20.8 +/- 3.4 to 12.2 +/- 1.5 pg/mg. By 12 h progesterone had dropped to 7.3 +/- 0.3 ng/mg whereas estrogen was undetectable by radioimmunoassay. Serum progesterone fell in 3 h from 5.53 +/- 0.39 to 3.15 +/- 0.26 ng/ml whereas estrogen fell from 172 +/- 26 to 123 +/- 9 pg/ml. The progesterone content of non-luteal ovarian tissue dropped in 3 h from 1.06 +/- 0.01 to 0.47 +/- 0.06 ng/mg and estrogen from 115.0 +/- 1.5 to 11.0 +/- 0.65 pg/mg. Both progesterone and estrogen were undetectable at 24 h. In the CL, free cholesterol concentration did not change significantly after A/S treatment, while esterified cholesterol increased from 2.82 +/- 0.14 to 4.14 +/- 0.25 mug/mg within 6 h and 5.52 +/- 0.17 mug/mg by 12 h. The results suggest that LH plays a critical role in the maintenance of CL of early pregnancy in the hamster and that deprivation of LH, even for periods as short as 3 h, significantly influences steroid production. The accumulation of cholesterol esters following LH-deprivation suggests that loss of cholesteryl esterase activity could be one of the events leading to luteolysis.