Cellular reaction on the intraperitoneal injection of four types of polylactide particulates

Our plain-English summary of Cellular reaction on the intraperitoneal injection of four types of polylactide particulates, by A. van Sliedregt, M. Knook, S.C. Hesseling, et al (Biomaterials, 1992).

The study

• Authors: A. van Sliedregt, M. Knook, S.C. Hesseling, H.K. Koerten, K. de Groot, C.A. van Blitterswijk
• Journal: Biomaterials
• Published: 1992;13(12):819-24
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Four types of polylactide particulates, P-L-LA 100, 250, 550 KD and a P-DL-LA 400 KD were injected into the peritoneal cavity of mice. The inflammatory reaction showed an increase in cell number (mainly neutrophilic granulocytes) up to 48 h after which the cell numbers decreased below the control (phosphate-buffered saline). All four polylactide particulates aggregated and intermingled with inflammatory cells. The aggregates remained throughout the investigation period of 6 months. Quantitative measurements showed that standardization of the particle form and size is essential. From this study and other experiments in which calcium phosphates and asbestos were injected intraperitoneally, it is concluded that the inflammatory response observed in the peritoneal cavity is related to the type of material injected and probably to form and size of the individual particles, but not to molecular weight.

In plain English

This was a laboratory experiment in mice on polylactide particles. Asbestos was not tested in it. The authors injected particles, supplied as 20 to 80 micrometres across, into the abdominal (peritoneal) cavity of female Swiss mice. Measured average maximum diameters ranged from 33.7 to 91.6 micrometres. They used four polylactides: three poly-L-lactides (100, 250 and 550 KD) and one poly-DL-lactide (400 KD). Three animals were used per material per time point, with salt solution as the control, and the mice were followed from 4 hours to 6 months. Up to 48 hours, more cells were collected from treated mice than from controls, mainly neutrophil granulocytes, and most after the 250 KD material. At 1 week the numbers fell below control values. The particles clumped together with inflammatory cells, became surrounded by fibrous tissue, and were still present at 6 months. The authors concluded that differences between the polylactides were moderate to small. They attributed these differences probably to the L versus DL type and to particle form rather than to molecular weight. They mentioned asbestos only when describing other studies.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: animal experiment (intraperitoneal injection in mice, followed over time)
• Who was studied: Swiss SPF female mice weighing 22-32 g, from Harlan Zeist, The Netherlands. Three mice per material per time point, plus three control mice given phosphate-buffered saline. Time points ran from 4 hours to 6 months.
• Exposure: Polylactide particulates, supplied as 20-80 micrometres in diameter: P-L-LA 100 KD, P-L-LA 250 KD, P-L-LA 550 KD and P-DL-LA 400 KD. Measured mean maximum diameters before injection were 33.7 to 91.6 micrometres. The particles were suspended in phosphate-buffered saline at 10 mg/ml, and 1 ml was injected. No asbestos was injected in this study.
• Main results:
  • Before injection, mean maximum diameters ranged from 33.7 micrometres (P-L-LA 100 KD) to 91.6 plus or minus 31.2 micrometres (P-L-LA 250 KD), above the supplied range of 20-80 micrometres.
  • Up to 48 hours, cell numbers from polylactide-injected mice were higher than from saline controls. The highest numbers followed injection of P-L-LA 250 KD.
  • At 1 week, cell numbers for all four polylactides fell below the control value.
  • Neutrophil granulocytes were the main cells shortly after injection. By 1 week, most cells were foreign body giant cells, monocytes and fibroblasts.
  • All four materials formed particle aggregates in the peritoneal cavity by 4 hours.
  • Small groups of particles and foreign body giant cells became surrounded by fibrous tissue.
  • Particles were still present at 6 months. Degradation was hardly visible by light microscopy, but electron microscopy showed signs of degradation for all four polylactides.
  • The polylactide made up roughly 15 to 40% of aggregate sections for all four materials, with no clear relation to time after injection.
  • Before injection, P-L-LA 250 KD had the lowest form factor (0.53, meaning least round) and by far the largest maximum diameter (91.6 micrometres).
• The authors' conclusion: The authors concluded that only moderate-to-small differences in inflammatory reaction between the polylactides were seen. They concluded these differences were probably caused by the DL versus L type and the form of the particles rather than molecular weight. They also concluded that particle form and size must be standardized for quantitative study of degradation.
• Limitations the authors state:
  • The authors could not determine whether particle form or larger surface area was the more important cause of the increased cell response.
  • It was unclear how much physical damage to the peritoneum from the needle shape of P-L-LA 250 KD caused the increased short-term effect.
  • The particle measurements could not show whether degradation had occurred. Measurements had high standard deviations because sections cut through particles at different levels.

Topics

Medical terms in this study, explained in our Lexicon: Peritoneal Cavity.

Related studies

• Pathogenesis of mesothelial reactions to asbestos fibers. Monocyte recruitment and macrophage activation — R.M. Branchaud, L.J. Garant, et al. (1993)
• Acute and chronic effects of intraperitoneal injection of two types of asbestos in rats with a study of the histopathogenesis and ultrastructure of resulting mesotheliomas — M.L. Shin, H.I. Firminger (1973)
• Analysis of particles from hamster lungs following pulmonary talc exposures: implications for pathogenicity — E. Sato, S.A. McDonald, et al. (2020)
• Ultrastructure of mesothelial regeneration after intraperitoneal injection of asbestos fibres on rat omentum — S. Gonzalez, J. Friemann, et al. (1991)
• Mesothelioma dose response following intraperitoneal injection of mineral fibres — J.M. Davis, R.E. Bolton, et al. (1991)
• Mth1 deficiency provides longer survival upon intraperitoneal crocidolite injection in female mice — S. Funahashi, Y. Okazaki, et al. (2020)

Browse more research in Biomaterials, or return to medical research.