Momordica charantia (bitter melon) inhibits primary human adipocyte differentiation by modulating adipogenic genes

Abstract

Background: Escalating trends of obesity and associated type 2 diabetes (T2D) has prompted an increase in the use of alternative and complementary functional foods. Momordica charantia or bitter melon (BM) that is traditionally used to treat diabetes and complications has been demonstrated to alleviate hyperglycemia as well as reduce adiposity in rodents. However, its effects on human adipocytes remain unknown. The objective of our study was to investigate the effects of BM juice (BMJ) on lipid accumulation and adipocyte differentiation transcription factors in primary human differentiating preadipocytes and adipocytes.

Methods: Commercially available cryopreserved primary human preadipocytes were treated with and without BMJ during and after differentiation. Cytotoxicity, lipid accumulation, and adipogenic genes mRNA expression was measured by commercial enzymatic assay kits and semi-quantitative RT-PCR (RT-PCR).

Results: Preadipocytes treated with varying concentrations of BMJ during differentiation demonstrated significant reduction in lipid content with a concomitant reduction in mRNA expression of adipocyte transcription factors such as, peroxisome proliferator-associated receptor gamma (PPARgamma) and sterol regulatory element-binding protein 1c (SREBP-1c) and adipocytokine, resistin. Similarly, adipocytes treated with BMJ for 48 h demonstrated reduced lipid content, perilipin mRNA expression, and increased lipolysis as measured by the release of glycerol.

Conclusion: Our data suggests that BMJ is a potent inhibitor of lipogenesis and stimulator of lipolysis activity in human adipocytes. BMJ may therefore prove to be an effective complementary or alternative therapy to reduce adipogenesis in humans.

Figure 1

Cytotoxicity of bitter melon juice in human predaipocytes and adipocytes. Higher concentrations of BMJ, 5% and 10%, significantly increased LDH release and reduced total ATP levels in both, differentiating preadipocytes and adipocytes. Lower concentrations of BMJ, 0.5% to 2%, did not affect cell viability or cell proliferation in either differentiating preadipocytes or adipocytes. (A) LDH release and (B) cellular ATP levels in preadipocytes treated with BMJ during differentiation. Similarly, LDH release and cellular ATP levels in adipocytes treated with BMJ for 48 h, is depicted in Figures 1D and 1E, respectively. Values represent the mean ± SE (n = 6) of three independent experiments conducted in duplicate. ^{a, b, c, d}Mean values with common letters do not differ (p < 0.05).

Figure 2

Effect of bitter melon juice on cellular lipid droplets. Total cellular lipid contents were significantly reduced in preadipocytes undergoing differentiation when treated with varying concentrations of BMJ (Figures 2A - 2C). Light microscopic pictures of oil red 'O' staining in untreated control adipocytes (A), and preadipocytes treated with - 0.5% BMJ (B), 1% BMJ (C) or 2% BMJ (D), during differentiation (40× magnification). Figure 1E depicts degree of preadipocyte differentiation during treatment as measured by total amount of extracted oil "O" red. Values represent the mean ± SE (n = 6) of three independent experiments conducted in duplicate. ^{a, b, c, d}Mean values with common letters do not differ (p < 0.05).

Figure 3

Effect of bitter melon juice on cellular triglyceride mass. Cellular triglyceride levels were reduced in (A) differentiating preadipocytes treated with varying concentrations of BMJ during differentiation and (B) adipocytes treated with varying concentrations of BMJ for 24 and 48 h. Figure 3C depicts the increased release of glycerol into the media, when adipocytes were treated with varying concentration of BMJ (0.5% to 2%, v/v) for 24 and 48 h. Values represent the mean ± SE (n = 6) of three independent experiments conducted in duplicate. ^{a, b, c, d}Mean values with common letters do not differ (p < 0.05).

Figure 4

Effect of bitter melon juice on PPARγ mRNA expression. Differentiating preadipocytes treated with varying concentrations of BMJ demonstrate a significant reduction in PPARγ mRNA gene expression. Bar graphs depict the densitometry scans of PPARγ amplicons (348-bp) and are expressed as a ratio to GAPDH amplicon (298-bp) intensity. Data are expressed as a percentage of the control (set as 100%) and the values represent the mean ± SE (n = 6) of three independent experiments analyzed in duplicate. ^{a, b, c}Mean values with common letters do not differ (p < 0.05).

Figure 5

Effect of bitter melon juice on SREBP-1c mRNA expression. Differentiating preadipocytes treated with varying concentrations of BMJ (0.5% to 2%, v/v) demonstrate a significant reduction in SREBP-1c mRNA gene expression. Bar graphs depict the densitometry scans of SREBP gene amplicons (238-bp) and are expressed as a ratio to GAPDH amplicon (298-bp) intensity. Data are expressed as a percentage of the control (set as 100%) and the values represent the mean ± SE (n = 6) of three independent experiments analyzed in duplicate. ^{a, b, c}Mean values with common letters do not differ (p < 0.05).

Figure 6

Effect of bitter melon juice on resistin mRNA expression. Differentiating preadipocytes treated with varying concentrations of BMJ (0.5% to 2%, v/v) demonstrate a significant reduction in resistin mRNA gene expression. Bar graphs depict the densitometry scans of resistin gene amplicons (145-bp) and are expressed as a ratio to GAPDH amplicons (298-bp) intensity. Data are expressed as a percentage of the control (set as 100%) and the values represent the mean ± SE (n = 6) of three independent experiments analyzed in duplicate. ^{a, b, c}Mean values with common letters do not differ (p < 0.05).

Figure 7

Effect of bitter melon juice on perilipin mRNA expression. Adipocytes treated with varying concentrations of BMJ (0.5% to 2%, v/v) demonstrate a significant reduction in perilipin mRNA gene expression. Bar graphs depict the densitometry scans of 120-bp perilipin gene amplicons and are expressed as a ratio to GAPDH amplicon (298-bp) intensity. Data are expressed as a percentage of the control (set as 100%) and the values represent the mean ± SE (n = 6) of three independent experiments analyzed in duplicate. ^{a, b, c}Mean values with common letters do not differ (p < 0.05).