The mechanism of experimental adipocere formation: hydration and dehydrogenation in microbial synthesis of hydroxy and oxo fatty acids

Waxing Grave About Adipocere: Soft Tissue Change in an Aquatic Context

When postmortem environmental conditions are "just right," according to the "Goldilocks Phenomenon," soft tissues (and associated fatty acids) are converted into and preserved as adipocere. To better understand this conversion process and the development of adipocere three human cadavers were immersed in outside, water-filled pits for over 3 months to observe adipocere formation in an underwater context simulating actual field conditions. Recordings of environmental conditions showed that temperatures were between 21 degrees C and 45 degrees C, a range sufficient for the growth of Clostridium perfringens. Chemical analysis of liquid and tissue samples revealed an increase in palmitic acid and decrease in oleic acid. This study tracked the remarkable gross morphological changes that can occur in human bodies subjected to an aquatic postmortem environment. The results support the "Goldilocks Phenomenon" and substantiate previous findings that the presence of bacteria and water is crucial for adipocere to form.

The identification of adipocere in grave soils

Soil samples recovered from grave exhumations have been analysed in an attempt to identify and characterise adipocere contained in the samples. The soil samples were collected from different environments, including samples recovered from forensic grave sites. Gas chromatography-mass spectrometry (GC-MS) was employed to identify adipocere and characterise the fatty acid composition. X-ray diffraction was used to characterise the soil environments.

The mechanism of human adipocere formation

In adipocere, some specific fatty acids possessing higher melting points, together with soap, play an important role in the formation and stabilization of adipocere. These fatty acids were shown to be mainly 10-hydroxy stearic and 10-hydroxy palmitic acids. Slight amounts of 10-oxo stearic and 10-oxo palmitic acids, which have higher melting points than those of hydroxy fatty acids (OHFAs), exist in the adipocere as well. The substantial adipocere is formed and stabilized mainly by these specific fatty acids. The OHFA and oxo fatty acid (OXOFA) are biosynthesized by some bacterial enzymes. Various aerobic and anaerobic bacteria are involved in the formation of adipocere. For instance, microbial conversion of various unsaturated fatty acids to 10-OHFA by Micrococcus luteus was investigated. It turned out that 10-OHFA was synthesized only from fatty acids possessing cis-9-unsaturatin. It was also shown that 10-OHFAs were converted to the corresponding 10-OXOFAs but 10-OXO compounds were inactive as substrates. It was further found that the enzyme preparations from Flavobacterium meningosepticum solubilized by sonication catalyzed not only hydration of oleic acid to produce 10-hydroxy stearic acid, but also dehydrogenation of this product in the presence of deuterium. On the other hand, we found out that there was 10-hydroxy-12-octadecenoic acid (10-OHODA) in the linoleic acid in human adipocere and that there were 9-chloro-10-methoxy (9-methoxy-10-chloro) palmitic acid and 9-chloro-10-methoxy (9-methoxy-10-chloro) stearic acid in human neonate adipocere.

Epicoprostanol found in adipocere from five human autopsies

Adipocere formation is well known as a later postmortem change. We collected adipocere from five male victims which had been submerged under the sea or fresh water for 1 mon to 4 yr. Fresh subcutaneous fat of a male victim who died from a cerebral contusion was used as the control. The samples were homogenized, and the lipids were extracted with chloroform and methanol followed by injection into a gas chromatograph and a gas chromatograph-mass spectrometer. We detected hydroxy fatty acids (10-hydroxyoctadecanoic acid and 10-hydroxyhexadecanoic acid) as well as 10-ketooctadecanoic acid in adipocere, but not in the control. In addition, we found for the first time a cholesterol-related peak with a molecular ion of 388 in adipocere and identified it as epicoprostanol, suggesting not only oxidation but also reduction had occurred during the formation of adipocere. In addition, we showed the time-course of epicoprostanol accumulation. The relationship between the time of adipocere formation and the characteristic lipid composition is discussed.

Investigations on the mechanism of adipocere formation and its relation to other biochemical reactions

In the adipocere, which is one of the postmortem changes, some specific fatty acids possessing higher melting points, together with soap, play an important role in the formation of adipocere. These fatty acids were shown to be mainly 10-hydroxystearic and 10-hydroxypalmitic acids. Moreover, slight amounts of 10-oxostearic and 10-oxopalmitic acids, which have higher melting points than those of hydroxy fatty acids, exist in the adipocere as well. The substantial adipocere is formed and stabilized by these specific fatty acids together with the soap. The hydroxy fatty acid (OHFA) and oxo fatty acid (OXOFA) are biosynthesized by some bacterial enzymes. Various aerobic and anaerobic bacteria are involved in the formation of adipocere. For example, microbial conversion of various unsaturated fatty acids to 10-OHFA by Micrococcus luteus was investigated. It turned out that 10-OHFA was synthesized only from fatty acids possessing cis-9-unsaturation. It was also shown that 10-OHFAs were converted to the corresponding 10-OXOFAs but the 10-OXO compounds were inactive as substrates. Furthermore, it was found that the enzyme preparations from Flavobacterium meningosepticum solubilized by sonication catalyzed not only hydration of oleic acid to produce 10-hydroxystearic acid, but also dehydrogenation of this product in the presence of deuterium. On the other hand, we found out that there was 10-hydroxy-12-octadecenoic acid (10-OHODA) from linoleic acid in some kinds of adipocere. Recently, 10-epoxy-12-octadecenoic acid (leukotoxin, LTx), which is one of the lipid peroxides, was found not only in rice plants but in polymorphonuclear leukocytes. Since LTx was found in leukocytes related to inflammatory response, interest has been focused on its involvement, not only in the basic mechanism of biological defense, but also on the mechanism of shock as a vasoactive substance. A postmortem change itself is only remotely associated with a phenomenon in a living body. However, 10-OHODA found in adipocere seemed to exist also in polymorphonuclear leukocytes, suggesting that this compound might be closely related to a biological reaction.

Identification of the peroxidation product hydroxystearic acid in Lewis lung carcinoma cells

Whole cell lipids were extracted from the Lewis lung carcinoma in vitro line C108. The fatty acids were derivatized to methylesters in order to identify endogenous oxidized derivatives by gasmass spectroscopy. The presence of 9-hydroxystearic acid and 10-hydroxystearic acid was thus evidenced for the first time in cultured mammalian cells. Moreover a linear correlation was found between the concentration of these products expressed as percentage of total fatty acid methylesters and the cell density in tissue culture flasks. This finding suggests an involvement of hydroxystearic acid in cellular functions related to the cell density in monolayer cultures.